STORAGE AREA

NETWORKS
18CS822
8th SEM – AY : 2022-23
 MODULE 1
STORAGE SYSTEM
Introduction to Information
Storage

• Information storage is a
central pillar of information
technology.
• Useful data – Information
• Aim of Information Storage
– Business and profit
 Why Information management ?
• We live in on-command, on-demand world that means we need
information when and where it is required.

• We access the Internet every day to perform searches, participate

in social networking, send and receive e-mails, share pictures and
videos, and scores of other applications. Equipped with a growing
number of content-generating devices, more information is being
created by individuals than by businesses.

• The importance, dependency, and volume of information for the

business world also continue to grow at astounding rates.
• Businesses depend on fast and reliable access to information critical
to their success.

• Some of the business applications that process information include

airline reservations, telephone billing systems, e-commerce, ATMs,
product designs, inventory management, e-mail archives, Web
portals, patient records, credit cards, life sciences, and global capital
markets.

• The increasing criticality of information to the businesses has

amplified the challenges in protecting and managing the data.

• Organizations maintain one or more data centers to store and

manage information.

• A data center is a facility that contains information storage and

other physical information technology (IT) resources for computing,
networking, and storing information.
 Information Storage
• Businesses use data to derive information that is
critical to their day-to-day operations.
• Storage is a repository that enables users to store
and retrieve this digital data.
• Data - Data is a collection of raw facts from which
conclusions may be drawn.

• Eg: a printed book, a family photograph, a movie

on videotape, e-mail message, an e-book, a
bitmapped image, or a digital movie are all
examples of data.
• The data can be generated using a computer and
stored in strings of 0s and 1s, is called digital data
and is accessible by the user only after it is processed
by a computer.
The following is a list of some of the factors that
have contributed to the growth of digital data :
1. Increase in data processing capabilities
 Modern-day computers provide a significant increase in
processing and storage capabilities.
 This enables the conversion of various types of content
and media from conventional forms to digital formats.
2. Lower cost of digital storage
 Technological advances and decrease in the cost of
storage devices have provided low-cost solutions and
encouraged the development of less expensive data
storage devices.
 This cost benefit has increased the rate at which data
is being generated and stored.
3. Affordable and faster communication technology

 The rate of sharing digital data is now much faster than

traditional approaches.
 A handwritten letter may take a week to reach its
destination, whereas it only takes a few seconds for an
e-mail message to reach its recipient.

4. Proliferation of applications and smart devices

 Smartphones, tablets, and newer digital devices, along
with smart applications, have significantly contributed
to the generation of digital content.
 Types of Data
Structured data

 Structured data is organized in rows and columns in a rigidly defined

format so that applications can retrieve and process it efficiently.
 Structured data is typically stored using a database management system
(DBMS).

Unstructured data

 Data is unstructured if its elements cannot be stored in rows and columns,

and is therefore difficult to query and retrieve by business applications.
 Example: e-mail messages, business cards, or even digital format files such
as .doc,
 .txt, and .pdf.
 Big Data
• Big data refers to data sets whose sizes are
beyond the capability of commonly used
software tools to capture, store, manage, and
process within acceptable time limits.

• It includes both structured and unstructured data

• Variety of sources, including business application

transactions, web pages, videos, images, e-mails,
social media, and so on.
The big data ecosystem consists of the following:

1. Devices that collect data from multiple locations and also

generate new data about this data (metadata).

2. Data collectors who gather data from devices and users.

3. Data aggregators that compile the collected data to extract

meaningful information.

4. Data users and buyers who benefit from the information

collected and aggregated by others in the data value chain .
Figure: Big Data Ecosystem
Big data Analysis in real time requires new
techniques, architectures, and tools that provide :
1. high performance,
2. massively parallel processing (MPP) data
platforms,
3. advanced analytics on the data sets.

Big data Analytics provide an opportunity to

translate large volumes of data into right
decisions.
 Information
• Data, whether structured or unstructured, does not fulfil any purpose for
individuals or businesses unless it is presented in a meaningful form.

• Information is the intelligence and knowledge derived from data.

• Businesses analyze raw data in order to identify meaningful trends. On

the basis of these trends, a company can plan or modify its strategy.
•
• For example, a retailer identifies customers’ preferred products and
brand names by analyzing their purchase patterns and maintaining an
inventory of those products.

• Because information is critical to the success of a business, there is an

ever present concern about its availability and protection.
 Storage
• Data created by individuals or businesses must be stored so that it is
easily accessible for further processing.

• In a computing environment, devices designed for storing data are

termed storage devices or simply storage.

• The type of storage used varies based on the type of data and the rate at
which it is created and used.

• Devices such as memory in a cell phone or digital camera, DVDs, CD-

ROMs, and hard disks in personal computers are examples of storage
devices.

• Businesses have several options available for storing data including

internal hard disks, external disk arrays and tapes.
 Evolution of Storage Architecture
• Organizations had centralized computers (mainframe) and information storage
devices (tape reels and disk packs) in their data center.

• The evolution of open systems and the affordability and ease of deployment that
they offer made it possible for business units/departments to have their own
servers and storage.

• In earlier implementations of open systems, the storage was typically internal to

the server. This approach is referred to as server-centric storage architecture

• In this server-centric storage architecture, each server has a limited number of

storage devices, and any administrative tasks, such as maintenance of the server
or increasing storage capacity, might result in unavailability of information.

• Drawbacks : The rapid increase in the number of departmental servers in an

enterprise resulted in unprotected, unmanaged, fragmented islands of information
and increased capital and operating expenses.
 Information-Centric Architecture,
• In information-centric architecture, storage devices are managed centrally and
independent of servers.

• These centrally-managed storage devices are shared with multiple servers.

• When a new server is deployed in the environment, storage is assigned from the
same shared storage devices to that server.

• The capacity of shared storage can be increased dynamically by adding more

storage devices without impacting information availability.

• Advantages : Information management is easier and cost-effective.

• Storage technology and architecture continues to evolve, which enables

organizations to consolidate, protect, optimize, and leverage their data to achieve
the highest return on information assets.
 Data Center Infrastructure
• Organizations maintain data centers to provide centralized data
processing capabilities across the enterprise.

• The data center infrastructure includes computers, storage systems,

network devices, dedicated power backups, and environmental
controls (such as air conditioning and fire suppression).

Key Data Center Elements

1. Application: An application is a computer program that provides

the logic for computing operations. Eg: order processing system
2. Database: More commonly, a database management
system (DBMS) provides a structured way to store
data in logically organized tables that are interrelated.
A DBMS optimizes the storage and retrieval of data.
3. Host or compute: A computing platform (hardware,
firmware, and software) that runs applications and
databases.
4. Network: A data path that facilitates communication
among various networked devices.
5. Storage array: A device that stores data persistently
for subsequent use.
Example of an online order transaction system
 Key characteristics for Data Center
• Availability Elements
• Security

• Scalability

• Performance

• Data integrity

• Capacity

• Manageability
 Managing a Data Centre
1. Monitoring - continuous collection of information
and review of entire data center infrastructure.
Include
• security, performance, accessibility and capacity.
2. Reporting - done periodically on resource
performance, capacity and utilization.
3. Provisioning - providing h/w, s/w and other
resources to run the data center.

• Includes capacity and resource planning.

 Virtualization and Cloud Computing
• Virtualization is a technique of abstracting
physical resources, such as compute, storage
and network, and making them appear as
logical resources.
• Eg : Partitioning of raw disks.
• It provides pooling of physical resources.
• Aggregated view
• Centralized management of pooled resources.
• Virtual Resources share pooled physical
resources, improves the utilization of physical
IT resources.
• This in turn
– Saves cost
– Utilize less space and energy
– Better economics
– Green computing
• Rapid expansion and upgrade of resources leads
to challenges.
• This challenges is addressed by Cloud computing
• Cloud computing enables individuals or
businesses to use IT resources as service over the
network.
• It provides highly scalable and flexible computing.
• Enables provisioning of resources on demand.
• Cloud infrastructure is built upon virtualized data
centres.
• It enables consumption – based metering.
 CHAPTER 2
DATA CENTER ENVIRONMENT
• Evolution - Classic data center to virtualized data
center (VDC)
• Physical resources are pooled together and
provided as Virtual Data Center.
• This reduces total cost of owning an
infrastructure.
• VDC, virtual resources are created using software
that enables faster deployment compared to
CDC.
 APPLICATION
• An application is a computer program that
provides the logic for computing operations.
• Sends request to OS -> READ / WRITE (R/W)
Operations on storage devices.
• Application is layered on db which inturn uses
the OS to perform R/W operation on storage
devices.
 Categories of Applications
• Business Applications
• Infrastructure Management Applications
• Data Protection Applications and
• Security Applications

Eg : email, enterprise resource planning,

decision support system, authentication and
antivirus applications and so on
 Database Management System
(DBMS)
• A database is structured way to store data in
logically organized tables that are interrelated.
• Help to Optimize storage and retrieval of data.
• Controls – Creation, Maintenance and Use of
database.
• DBMS – processes data request -> transfers
data from storage
 Host (Compute)
• The computers on which applications run (database app)
are referred to as hosts or compute systems.
• Host can be Physical or virtual
• A compute virtualization software enables creating virtual
machines on top of physical compute infrastructure.
• Eg : Physical hosts – desktop, server, mobile devices
• A host – CPU, memory, I/O Devices and s/w to perform
computing operations.
• This s/w includes OS, File systems, device drivers
• This s/w can be installed as separate entity or as a part of
OS.
 Host (Compute)
• Operating System
• Device Driver
• Volume Manager
• File System
 Operating System
• Controls all aspects of computing
• Works between physical components and
applications
• Service – data access
• Responds to user actions and the environment
• Organizes, controls h/w and manages allocation
of resources.
• Provides security to resource usage
• Storage management
• In virtualized environment, virtualization works between OS and
h/w resources.
• In this OS performs activities related to application interaction.
• H/w management is handles by virtualized layer.
• Memory Virtualization – virtualizes the physical memory (RAM)
of a host.
• Virtual Memory Manager (VMM) – OS utility
– Virtual to physical memory mapping
– Swap space / swap file
– Memory of system is divided into contiguous blocks of fixed sized
pages.
– Paging – moves inactive physical memory onto the swap file and
brings them back to physical memory when required.
– Paging – efficient use of physical memory.
– OS moves LUP into swap file, so RAM is available for more active
processes.
 Device Driver
• Special s/w that permits OS to interact with a
specific device.
• Eg : printer, disk drives, mouse etc
• Enables the OS to recognize the device
• To access and control devices
• H/w dependent
• OS specific
 Volume Manager
• Traditional systems had disk drives that
appeared to OS as a number of continuous
disk blocks.
• Disadvantages :
– Lack of flexibility
– No easy way to extend file system’s size
– Under utilization of storage capacity – allocating
entire disk for file systems
• Logical Volume Manager (LVMs)
– Dynamic extension of FS capacity
– Efficient storage management
– It is s/w that runs on compute systems
– It manages logical and physical storage
– It is an intermediate layer between FS and physical
disk.
– Partition larger disk into virtual smaller capacity
volumes (Partitioning)
– Aggregate smaller disks to form larger virtual
volume. (Concatenation)
• Disk Partitioning
– Flexibility
– Utilization of disk drives
– Disk drives divided into logical containers called as
Logical Volumes (LVs).
– Maintain data according to file systems and
application requirements.
• Disk Concatenation
– Grouping several physical drives – presenting to host
as one big logical volume
– LMV provides optimized storage access and simplifies
storage management
– Administrators can change storage allocation even
when the application is running.
Basics LVM Components :
• Physical volumes
• Volume groups
• Logical volumes
Physical Volume Identifier (PVID) is assigned to each
physical volume.
• PV can be added or removed dynamically
• But cannot be shared among Volume Groups
• Physical extent – Each PV is partitioned into
equal sized data blocks
• A volume group have a number of Logical
Volumes in it.
• A file system is created on a logical volume.
• These volumes are then assigned to
applications.
 FILE SYSTEM
• A file is a collection of related records or data
stored as a unit with a name.
• A file system is a hierarchical structure of files.
• File system consists of logical structures and
software routines that control access to files.
• File permissions
• Organizes data in structured hierarchical manner.
• Metadata
• File servers manage and share a large number of
files over a network.
 1. Connectivity

 Connectivity refers to the interconnection between hosts or

between a host and peripheral devices, such as printers or
storage devices.
 Connectivity and communication between host and storage are
enabled using:
 physical components
 interface protocols.
 Interface Protocols

 A protocol enables communication between the host and

storage.
 Protocols are implemented using interface devices (or
controllers) at both source and destination.
 The popular interface protocols used for host to storage
communications are:
i. Integrated Device Electronics/Advanced Technology Attachment (IDE/ATA)
ii. Small Computer System Interface (SCSI),
iii. Fibre Channel (FC)
iv. Internet Protocol (IP)
IDE/ATA and Serial ATA:
 IDE/ATA is a popular interface protocol standard used for connecting
storage devices, such as disk drives and CD-ROM drives.
 This protocol supports parallel transmission and therefore is also known
as Parallel ATA (PATA) or simply ATA.
 IDE/ATA has a variety of standards and names.
 The Ultra DMA/133 version of ATA supports a throughput of 133 MB per
second.
 In a master-slave configuration, an ATA interface supports two storage
devices per connector.
 If performance of the drive is important, sharing a port between two devices
is not recommended.
 The serial version of this protocol is known as Serial ATA (SATA) and
supports single bit serial transmission.
 High performance and low cost SATA has replaced PATA in newer systems.
 SATA revision 3.0 provides a data transfer rate up to 6 Gb/s.
SCSI and Serial SCSI:
 SCSI has emerged as a preferred connectivity protocol in high-end
computers.
 This protocol supports parallel transmission and offers improved
performance, scalability, and compatibility compared to ATA.
 The high cost associated with SCSI limits its popularity among home
or personal desktop users.
 SCSI supports up to 16 devices on a single bus and provides data
transfer rates up to 640 MB/s.
 Serial attached SCSI (SAS) is a point-to-point serial protocol that
provides an alternative to parallel SCSI.
 A newer version of serial SCSI (SAS 2.0) supports a data transfer rate up
to 6 Gb/s.
 Fibre Channel (FC):
 Fibre Channel is a widely used protocol for high-speed
communication to the storage device.
 Fibre Channel interface provides gigabit network speed.
 It provides a serial data transmission that operates over
copper wire and optical fiber.
 The latest version of the FC interface (16FC) allows
transmission of data up to 16 Gb/s.
Internet Protocol (IP):
 IP is a network protocol that has been traditionally used for host-to-host traffic.

 With the emergence of new technologies, an IP network has become a viable

option for host- to-storage communication.
 IP offers several advantages:
 cost
 Maturity
enables organizations to leverage their existing IP-based network.

 iSCSI and FCIP protocols are common examples that leverage IP for host-to-storage
communication.
 Storage

 Storage is a core component in a data center.

 A storage device uses magnetic, optic, or solid state media.
 Disks, tapes, and diskettes use magnetic media,
 CD/DVD uses optical media.
 Removable Flash memory or Flash drives uses solid state media.
 Tapes
 In the past, tapes were the most popular storage option for backups because of their
low cost.
 Tapes have various limitations in terms of performance and management, as listed
below
i. Data is stored on the tape linearly along the length of the tape. Search and retrieval of data
are done sequentially, and it invariably takes several seconds to access the data. As a
result, random data access is slow and time-consuming.
ii. In a shared computing environment, data stored on tape cannot be accessed by multiple
applications simultaneously, restricting its use to one application at a time.
iii. On a tape drive, the read/write head touches the tape surface, so the tape degrades or
wears out after repeated use.
iv. The storage and retrieval requirements of data from the tape and the overhead
associated with managing the tape media are significant.
 Due to these limitations and availability of low-cost disk drives, tapes are no longer a
preferred choice as a backup destination for enterprise-class data centers.
 Optical Disc Storage:
 It is popular in small, single-user computing environments.
 It is frequently used by individuals to store photos or as a backup medium on personal or
laptop computers
 It is also used as a distribution medium for small applications, such as games, or as a means
to transfer small amounts of data from one computer system to another.
 The capability to write once and read many (WORM) is one advantage of optical disc
storage. Eg: CD-ROM
 Collections of optical discs in an array, called a jukebox, are still used as a fixed-content
storage solution.
 Other forms of optical discs include CD-RW, Blu-ray disc, and other variations of DVD.
 Disk Drives:
 Disk drives are the most popular storage medium used in modern computers for storing
and accessing data for performance-intensive, online applications.
 Disks support rapid access to random data locations.
 Disks have large capacity.
 Disk storage arrays are configured with multiple disks to provide increased capacity
and
enhanced performance.
 Disk drives are accessed through predefined protocols, such as ATA, SATA, SAS, and FC.
 These protocols are implemented on the disk interface controllers.
 Disk interface controllers were earlier implemented as separate cards, which were
connected to the motherboard.
 Modern disk interface controllers are integrated with the disk drives; therefore, disk drives
are known by the protocol interface they support, for example SATA disk, FC disk, etc.
Basic Disc Drive Components
•Platter – it is a circular disk that the data is recorded on in binary codes. The typical
HDD cnsist of more than one platter
•Spindle – a spindle connects all the platters and is connected to a motor. The motor of the
spindle rotates with a constant speed (revolutions per minute). The most common speeds
are:
• 5400 rpm
• 7200 rpm
• 10000 rpm
• 15000 rpm
• Read/Write Head – Each platter have two R/W heads – one for each surface of the
platter. The R/W head changes the magnetic polarization on the surface of the platter when
writing data
•Actuator Arm Assembly – R/W heads are mounted to the actuator arm assembly, which
position the R/W head for the location on the platter where the data needs to be written or
read.
Disk Service Time

Seek Time
Also called access time. Seek Time describes the time taken to position the R/W head
across the platter with a radial movement (moving along the radius of the platter). So to
speak, seek time is the time taken to position and settle the arm and the head over the
correct track.

The average seek time on a modern disk is typically in the range of 3 to 15 milliseconds.

High seek time has a big impact on the read operation of random tracks. To minimize the
seek time, data can be written to only a part of available space in cylinders. This results in
lower usable capacity, and is known as short-stroking the drive.
 Rotational Latency
To access data, the actuator arm moves the R/W head over the platter to a particular track
while the platter spins to position the requested sector under the R/W head. The time taken
by the platter to rotate and position the data under the R/W head is called rotational
latency.
As you can notice, the average rotational latency depends on rpm of the disk. For example
and average rotational latency for 5,400-rpm disk is about 5.5 ms, while for a 15,000-rpm
disk is about 2.0 ms.
 Data Transfer Rate
In a read operation the data first moves from the disk platters to R/W heads. Then it moves
to the drive’s internal buffer. Finally data moves from the buffer thru the interface to the host
HBA.
In a write operation the data moves from the HBA to the internal buffer of the disk thru the
drive’s interface. The data then moves from the buffer to the R/W heads. Finally, it moves
from the R/W heads to the platters. The data transfer rate is the average amonut of data
per unit time that the drive can deliver to the HBA
 Internal Transfer Rate
Internatl transfer rate is the speed at which data moves from platter’s surface to the internal
buffer (cache) of the disk.
Host Access to Storage
Direct Attached Storage
 Storage Design Based on Application
Requirements and Disk Performance
Ts = T + L + X
Ts – Disk Service Time
T – Sum of the seek time
L – Rotational Latency
X – Internal Transfer Time
Eg: Average Seek time is 5ms, disk rotation speed of 15,000 revolutions
per minute or 250 revolutions per second, L=(0.5/250 rps in ms)

40 MB/s internal data transfer rate, (internal transfer time X= 32KB / 40MB),
where block size of 32 KB (assume)
Ts = 5ms + (0.5/250) + 32 KB /40 MB
= 7.8 ms

Therefore maximum number of I/Os serviced

per second or IOPS is
(1/Ts) = 1 / (7.8 x 10-3) = 128 IOPS
Response Time, R increases with disk controller
utilization. If disk controller utilization is 96% for
I/O with block size of 32 KB.

R = Ts / (1-U) = 7.8 / (1 - 0.96)

= 195 ms
Total Number of disks required for an
application :
DR = MAX (Dc, Di)
 Module - 2

Data Protection - RAID

 Redundant Array of Independent Disks (RAID)
• A group of hard disks is called a disk array
• RAID combines a disk array into a single virtual
device
– called RAID drive
• Provide fault tolerance for shared data and
applications
• Different implementations: Level 0-5
• Characteristics:
– Storage Capacity
– Speed: Fast Read and/or Fast Write
– Resilience in the face of device failure
 RAID Implementation Methods
Software RAID
- uses host based software to provide RAID function.
- implemented at OS level.
- does not use a dedicated h/w controller to manage.
Advantages :
 Cost
 Simplicity

Limitations :
 Performance
 Supported features
 Operating system compatibility
Hardware RAID
• Controller Card RAID
• External RAID Controller
• Key Functions of RAID Controller:
– Management and control of disk aggregation
– Translation of I/O requests between logical disks
and physical disks
– Data regeneration in the event of disk failures
RAID ARRAY COMPONENT
 RAID Functions / Techniques
• Striping
– Write consecutive logical byte/blocks on consecutive physical disks
• Mirroring
– Write the same block on two or more physical disks
• Parity Calculation
– Given N disks, N-1 consecutive blocks are data blocks, Nth block is
for parity
– When any of the N-1 data blocks is altered, N-2 XOR calculations
are performed on these N-1 blocks
– The Data Block(s) and Parity Block are written
– Destroy one of these N blocks, and that block can be reconstructed
using N-2 XOR calculations on the remaining N-1 blocks
– Destroy two or more blocks – reconstruction is not possible
 XOR Operation
A B XOR
0 0 0
0 1 1
1 0 1
1 1 0
Disk Striping and Parity bits (example)
Example 1: 1 0 1 0 1 1

1 1 1 001 110

disk 1: odd bits disk 2: even bits parity bits (even parity)

Example 2: 1 0 1 0 1 1

1 0 01 11 00

3k+1 bits 3k+2 bits

3k bits parity bits (odd parity)
• RAID 0
RAID Types
– Stripe with no parity (see next slide for figure)
• RAID 1
– Mirror two or more disks
• RAID 0+1 (or 1+0)
– Stripe and Mirrors
• RAID 3
– Synchronous, Subdivided Block Access; Dedicated
Parity Drive
• RAID 4
– Stripe and Dedicated Parity Drive
• RAID 5
– Like RAID 4, but parity striped across multiple drives
 RAID 0 RAID 1

Disk Striping (no redundancy) Disk Mirror

RAID 0+1
(or 1+0)
 RAID 3 RAID
5

Disk striping with Dedicated Parity Drive Disk striping with Distributed Parity Data
Striping (parity) data is duplicate.
 Application IOPS and RAID configuration
• When describing the number of disk required for an application, it is
important to consider the impact of RAID based on IOPS generated by
the application.
• The total disk load should be computed by considering the type of RAID
configuration and the ratio of read compared to write from the host

• Consider an application that generates 5,200 IOPS, with 60 percent of

them being reads.
1) The disk load in RAID 5 is calculated as follows
RAID 5 disk load(read+write)=0.6*5200+4*(.4*5200) [because write
penalty for RAID 5 is 4]
=3120+4*2080
=3120+8320
=11440 IOPS
2) The disk load in RAID 1 is calculated as follows
RAID 5 disk load(read+write)=0.6*5200+2*(.4*5200) [because every write
manifests as two writes to disks]
=3120+2*2080
=3120+4160
=7280 IOPS
• In this example a disk drive with a specification of a maximum
180 IOPS needs to be used, the number of disks required to
meet the workload for the RAID configuration would be:

• RAID 5: 11440/180=64 disks

• RAIN 1: 7280/180=42 disks (approximated to the nearest even
number)
 Hot Spares
• Hot Spare refers to a spare drive in a RAID array.
• If Parity RAID is used the data is rebuild onto the hot spare from the
parity and the data on the surviving disk drives in the RAID set.
• If mirroring is used, the data from the surviving mirror is used to copy
the data onto the hot spare.
 Intelligent Storage Systems
• Intelligent Storage systems are feature-rich RAID arrays that
provide highly optimized I/O processing capabilities.
• These storage systems are configured with a large amount of
memory(called cache) and multiple I/O paths and use
sophisticated algorithms
• They have added new dimension to storage system performance,
scalability and availability.
Components of an Intelligent Storage
System
• Front End
• Cache
• Back end
• Physical disk
 Cache
Structure of Cache
• Read operation with cache
– Prefetch
– Fixed prefetch
– Variable prefetch
• Write operation with cache
– Write- back cache
– Write-through cache
• Write operation with cache
• Cache Implementation
• Dedicated Cache
• Global Cache
• Cache Management
• Least Recently used(LRU)
• Most Recently Used(MRU)
– Idle flushing
– High watermark flushing
– Forced flushing

• Cache Data Protection

• Cache mirroring
• Cache vaulting

• Back end
• Physical Disk
 Types of Intelligent Storage Systems
• High – End Storage System
• Midrange Storage System
• High – End Storage System
– Active – active Configuration
– Large storage capacity
– Large amount of cache to service host I/Os optimally
– Fault tolerance architecture to improve data availability
– Connectivity to mainframe computers and open systems
– Availability of multiple back end controllers to manage disk
processing
• Midrange Storage System
– Active – passive Configuration
High – End Storage System
Midrange Storage System
Fibre Channel Storage Area Networks
Fibre Channel: Overview
• The FC architecture forms the fundamental construct
of the SAN infrastructure.
• Fibre Channel is a high-speed network technology
that runs on high-speed optical fiber cables
(preferred for front-end SAN connectivity) and serial
copper cables (preferred for back-end disk
connectivity).
• The FC technology was created to meet the demand
for increased speeds of data transfer
 Components of FC SAN
• Components of FC SAN infrastructure are:
• Node Ports,
• Cabling,
• Connectors,
• Interconnecting Devices (Such As Fc Switches
Or Hubs),
• San Management Software.
 Node Ports
• In fibre channel, devices such as
hosts, storage and tape libraries
are all referred to as Nodes.
• Each node is a source or
destination of information for
one or more nodes.
• Each node requires one or more
ports to provide a physical
interface for communicating with
other nodes.
• A port operates in full-duplex
data transmission mode with a
transmit (Tx) link and a receive
(Rx) link.
 Cabling
• Multi-mode fiber (MMF) cable carries multiple
beams of light projected at different angles
simultaneously onto the core of the cable
• In an MMF transmission, multiple light beams
traveling inside the cable tend to disperse and
collide. This collision weakens the signal strength
after it travels a certain distance — a process
known as modal dispersion.
– MMFs are generally used within data centers for
shorter distance runs
• Single-mode fiber (SMF) carries a single ray of
light projected at the center of the core (see Fig
2.2 (b)).
– In an SMF transmission, a single light beam travels in a
straight line through the core of the fiber.
– The small core and the single light wave limits modal
dispersion. Among all types of fibre cables, single-
mode provides minimum signal attenuation over
maximum distance (up to 10 km).
– A single-mode cable is used for long-distance cable
runs, limited only by the power
Multimode fiber and single-mode fiber
 Connectors
 They are attached at the end of the cable to enable
swift connection and disconnection of the cable to and
from a port.
 A Standard connector (SC) (see Fig 2.3 (a)) and a
Lucent connector (LC) (see Fig 2.3 (b)) are two
commonly used connectors for fiber optic cables.
 An SC is used for data transmission speeds up to 1
Gb/s, whereas an LC is used for speeds up to 4 Gb/s.
SC,LC, and ST connectors
 Interconnect Devices
The commonly used interconnecting devices in SAN are

• Hubs - are used as communication devices in FC-AL implementations.

• Switches - are more intelligent than hubs and directly route data from
one physical port to another.
– Switches are available with:
• Fixed port count
• Modular design : port count is increased by installing additional port cards to open slots.

• Directors – are larger than switches and are deployed for data center
implementations.

– The function of directors is similar to that of FC switches, but directors have

higher port count and fault tolerance capabilities.
– Port card or blade has multiple ports for connecting nodes and other FC
switches
 SAN Management Software
• SAN management software manages the interfaces
between hosts, interconnect devices, and storage arrays.

• The software provides a view of the SAN environment and

enables management of various resources from one central
console.

• It provides key management functions, including mapping

of storage devices, switches, and servers, monitoring and
generating alerts for discovered devices, and logical
partitioning of the SAN, called zoning
 MODULE 3

IP SAN and FCoE

 iSCSI
• iSCSI is an IP based protocol that establishes and
manages connections between host and storage
over IP, as shown in Fig 2.21.
• iSCSI encapsulates SCSI commands and data into
an IP packet and transports them using TCP/IP.
• iSCSI is widely adopted for connecting servers
to storage because it is relatively inexpensive and
easy to implement, especially in environments in
which an FC SAN does not exist.
iSCSI implementation
 Components of iSCSI
– An initiator (host), target (storage or iSCSI gateway), and an IP-based
network are the key iSCSI components.
– If an iSCSI-capable storage array is deployed, then a host with the iSCSI
initiator can directly communicate with the storage array over an IP
network.
– However, in an implementation that uses an existing FC array for iSCSI
communication, an iSCSI gateway is used.
– These devices perform the translation of IP packets to FC frames and vice
versa, thereby bridging the connectivity between the IP and FC
environments.
iSCSI Host Connectivity
• The three iSCSI host connectivity options are:

• A standard NIC with software iSCSI initiator, a

TCP offload engine (TOE) NIC with software
iSCSI initiator,an iSCSI HBA

• The function of the iSCSI initiator is to route

the SCSI commands over an IP network
 iSCSI Topologies

• Two topologies of iSCSI implementations are

native and bridged
• Native iSCSI Connectivity
– FC components are not required for iSCSI connectivity if an
iSCSI-enabled array is deployed.
– In Fig 2.22(a), the array has one or more iSCSI ports configured
with an IP address and is connected to a standard Ethernet
switch.
– After an initiator is logged on to the network, it can access the
available LUNs on the storage array.
– A single array port can service multiple hosts or initiators as
long as the array port can handle the amount of storage traffic
that the hosts generate.
• Bridged iSCSI Connectivity

– A bridged iSCSI implementation includes FC components in its

configuration.

– The gateway converts IP packets to FC frames and vice versa.

– The bridge devices contain both FC and Ethernet ports to

facilitate the communication between the FC and IP
environments.
iSCSI Protocol Stack
– SCSI is the command protocol that works at the application layer of the Open
System Interconnection (OSI) model.

– The initiators and targets use SCSI commands and responses to talk to each
other.

– The SCSI command descriptor blocks, data, and status messages are
encapsulated into TCP/IP and transmitted across the network between the
initiators and targets.

– iSCSI is the session-layer protocol that initiates a reliable session

between devices that recognize SCSI commands and TCP/IP.

– The iSCSI session-layer interface is responsible for handling login,

authentication, target discovery, and session management.

– TCP is used with iSCSI at the transport layer to provide reliable transmission.
 iSCSI PDU

iSCSI PDU encapsulated in an IP packet

 iSCSI Discovery

• An initiator must discover the location of its

targets on the network and the names of the
targets available to it before it can establish a
session.
• This discovery can take place in two ways:

– SendTargets discovery

– internet Storage Name Service (iSNS).

Discovery using iSNS
 iSCSI Names

– iSCSI Qualified Name (IQN):

– Extended Unique Identifier (EUI)

iSCSI Session
Command Sequencing
 FCIP (Fibre channel over IP
• FCIP Protocol Stack
FCIP encapsulation
FCIP Topology
 FCoE (Fibre Channel over Ethernet)
• To support multiple networks, servers in a data center are equipped
with multiple redundant physical network interfaces

— for example, multiple Ethernet and FC cards/adapters. In

addition, to enable the communication, different types of networking
switches and physical cabling infrastructure are implemented in data
centers

• Fibre Channel over Ethernet (FCoE) protocol provides consolidation

of LAN and SAN traffic over a single physical interface infrastructure

• FCoE uses the Converged Enhanced Ethernet (CEE) link (10 Gigabit
Ethernet) to send FC frames over Ethernet
Before using FCOE
After using FCOE
•
Components of FCOE
The key components of FCOE are :
– Converged Network Adaptors(CNA)
– Cables
– FCOE Switches
Converged Network Adapter
FCoE switch generic architecture
 NETWORK ATTACHED STORAGE (NAS)
File Sharing Environment
• File sharing enables users to share files with other users

• In file-sharing environment, the creator or owner of a file determines the

type of access to be given to other users and controls changes to the file.
• Examples of file sharing methods:

– File Transfer Protocol (FTP)

– Distributed File System (DFS)

– Network File System (NFS) and Common Internet File System (CIFS)

– Peer-to-Peer (P2P)
 What is NAS?
• NAS is an IP based dedicated, high-
performance file sharing and storage device.

• Enables NAS clients to share files over an IP

network.

• Uses network and file-sharing protocols to

provide access to the file data
General Purpose Serves Versus NAS
 Benefits of NAS
• Comprehensive access to information
• Improved Efficiency
• Improved flexibility
• Centralized Storage
• Simplified Management
• Scalability
• High Availability
• Security
• Low cost
• Ease of deployment
 Components of NAS

• NAS device has two key components : NAS

head and storage.
NAS I/O Operation
 NAS Implementation
• Unified NAS
• Unifiedd NAS Connectivity
• Gateway NAS
• Gateway NAS Connectivity
• Scale – Out NAS
• Scale – Out NAS Connectivity
 NAS File Sharing Protocols
•Common Internet File System (CIFS)
•CIFS is a client-server application protocol

•It enables clients to access files and services on remote computers over TCP/IP.

•It is a public, or open, variation of Server Message Block (SMB) protocol.

•Network File System (NFS)

•NFS is a client-server protocol for file sharing that is commonly used on UNIX
systems.

•NFS was originally based on the connectionless User Datagram Protocol (UDP).

•It uses Remote Procedure Call (RPC) as a method of inter-process communication

between two computers.

•The NFS protocol provides a set of RPCs to access a remote file system
 Factors Affecting NAS Performance
• Number of hops
• Authentication with a directory service such
as Active Directory or NIS
• Retransmission
• Over utilized routers and switches
• File system lookup and metadata requests
• Over utilized NAS devices
• Over utilized clients
 MODULE 4

INTRODUCTION
TO
BUSINESS CONTINUITY
 Business Continuity (BC):
• Business continuity (BC) is an integrated and
enterprise wide process that includes all activities
(internal and external to IT) that a business must
perform to mitigate the impact of planned and
unplanned downtime.
• It involves proactive measures, such as business impact
analysis, risk assessments, deployment of BC
technology solutions (backup and replication), and
reactive measures, such as disaster recovery and
restart, to be invoked in the event of a failure.
• Goal : “information availability”
 Information Availability
Information availability (IA) refers to the ability of
the infrastructure to function according to business
expectations during its specified time of operation.

Information availability can be defined in terms of:

• Reliability,
• Accessibility
• Timeliness.
 Causes of Information Unavailability
• Planned outages
• Unplanned outages
• Disasters (natural or man-made)

Disruptors of Information Availability

 Consequences of Downtime
• Information unavailability or downtime results in loss of productivity, loss
of revenue, poor financial performance, and damage to reputation.

• Loss of productivity includes reduced output per unit of labor, equipment,

and capital.

• Loss of revenue includes direct loss, compensatory payments, future

revenue loss, billing loss, and investment loss.

• Poor financial performance affects revenue recognition, cash flow,

discounts, payment guarantees, credit rating, and stock price.

• Damages to reputations may result in a loss of confidence or credibility

with customers, suppliers, financial markets, banks, and business
partners.
• An important metric, average cost of downtime per hour, provides a
key estimate in determining the appropriate BC solutions. It is
calculated as follows:

Average cost of downtime per hour = average productivity loss per

hour + average revenue loss
per hour

Where:
Productivity loss per hour = (total salaries and benefits of all
employees per week) / (average number of working hours per week)

Average revenue loss per hour = (total revenue of an organization per

week) / (average number of hours per week that an organization is
open for business)
 Measuring Information Availability
• Mean Time Between Failure (MTBF): It is the average
time available for a system or component to perform
its normal operations between failures.
• Mean Time To Repair (MTTR): It is the average time
required to repair a failed component.
MTTR includes the total time required to do the
following activities:

Detect the fault, mobilize the maintenance

team, diagnose the fault, obtain the spare
parts, repair, test, and restore the data.
 Information availability metrics

IA = system uptime / (system uptime + system downtime)

In terms of MTBF and MTTR, IA could also be expressed as

IA = MTBF / (MTBF + MTTR)
Availability percentage and Allowable downtime
 BC Terminology

• Disaster recovery: This is the coordinated process of

restoring systems, data, and the infrastructure required to
support key ongoing business operations in the event of a
disaster.
• Disaster restart: This is the process of restarting business
operations with mirrored consistent copies of data and
applications.
• Recovery-Point Objective (RPO): This is the point in time to
which systems and data must be recovered after an outage.
It defines the amount of data loss that a business can
endure.
– A large RPO signifies high tolerance to information loss in a
business.
 Example :
• RPO of 24 hours: This ensures that backups are created on an
offsite tape drive every midnight. The corresponding recovery
strategy is to restore data from the set of last
backup tapes.

• RPO of 1 hour: Shipping database logs to the remote site every

hour. The corresponding recovery strategy is to recover the
database at the point of the last log shipment.

• RPO in the order of minutes: Mirroring data asynchronously to a

remote site

• Near zero RPO: This mirrors mission-critical data synchronously to a

remote site.
• Recovery-Time Objective (RTO): The time within which
systems and applications must be recovered after an
outage.
It defines the amount of downtime that a
business can endure and survive.

• RTO of 72 hours: Restore from backup tapes at a cold

site.
• RTO of 12 hours: Restore from tapes at a hot site.
• RTO of few hours: Use a data vault to a hot site.
• RTO of a few seconds: Cluster production servers with
bidirectional mirroring, enabling the applications to
run at both sites simultaneously.
BC Planning Life Cycle
• Establishing objectives
– Determine BC requirements.
– Estimate the scope and budget to achieve
requirements.
– Select a BC team by considering subject matter
experts from all areas of the business, whether
internal or external.
– Create BC policies.
• Collect information on data profiles, business
processes, infrastructure support,
dependencies, and frequency of using
business infrastructure.
– Identify critical business needs and assign
recovery priorities.
– Create a risk analysis for critical areas and
mitigation strategies.
– Conduct a Business Impact Analysis (BIA).
– Create a cost and benefit analysis based on the
consequences of data unavailability.
• Designing and developing
– Define the team structure and assign individual
roles and responsibilities. For example, different
teams are formed for activities such as emergency
response, damage assessment, and infrastructure
and application recovery.
– Design data protection strategies and develop
infrastructure.
– Develop contingency scenarios.
– Develop emergency response procedures.
– Detail recovery and restart procedures.
• Implementing
– Implement risk management and mitigation
procedures that include backup, replication, and
management of resources.
– Prepare the disaster recovery sites that can be
utilized if a disaster affects the primary data
center.
– Implement redundancy for every resource in a
data center to avoid single points of failure.
• Training, testing, assessing, and maintaining
– Train the employees who are responsible for backup and
replication of business-critical data on a regular basis or
whenever there is a modification in the BC plan
– Train employees on emergency response procedures when
disasters are declared.
– Train the recovery team on recovery procedures based on
contingency scenarios.
– Perform damage assessment processes and review
recovery plans.
– Test the BC plan regularly to evaluate its performance and
identify its limitations.
– Assess the performance reports and identify limitations.
– Update the BC plans and recovery/restart procedures to
reflect regular changes within the data center.
 Failure Analysis
• Single Point of Failure
– A single point of failure refers to the failure of
a component that can terminate the
availability of the entire system or IT service.
– The client is connected to the server through
an IP network, the server is connected to the
storage array through a FC connection, an HBA
installed at the server sends or receives data to
and from a storage array, and an FC switch
connects the HBA to the storage port
Single Point of Failure
 Resolving Single Points of Failure
• systems are designed with
redundancy
• Data centers follow
stringent guidelines to
implement fault tolerance
for uninterrupted
information availability.
 Multipathing Software
• Configuration of multiple paths increases the data
availability through path failover.
• Multiple paths to data also improve I/O performance through load
sharing and maximize server, storage, and data path utilization.

• Multipathing software provides the functionality to

recognize and utilize alternate I/O path to data.
• Multipathing software also manages the load balancing by
distributing I/Os to all available, active paths.
• Multipathing is enabled either by using the hypervisor’s
built-in capability or by running a third-party software
module, added to the hypervisor.
 BC Technology Solutions
1. Backup: Data backup is a predominant
method of ensuring data availability.
2. Storage array-based replication (local): Data
can be replicated to a separate location
within the same storage array.
3. Storage array-based replication (remote):
Data in a storage array can be replicated to
another storage array located at a remote
site.
 Backup and Archive
• Data Backup is a copy of production data,
created and retained for the sole purpose of
recovering lost or corrupted data.

• Data archiving is the process of moving data

that is no longer actively used, from primary
storage to a low-cost secondary storage.
 Backup Purpose
• Backups are performed to serve three purposes:
disaster recovery, operational recovery, and
archival.
• Disaster Recovery
– The backup copies are used for restoring data at
an alternate site when the primary site is
incapacitated due to a disaster. Based on RPO and
RTO requirements, organizations use different
backup strategies for disaster recovery.
• Operational Recovery
– Operational recovery is the use of backups to
restore data if data loss or logical corruption
occurs during routine processing
• Archival
• Traditional backups are still used by small and
medium enterprises for long-term preservation of
transaction records, e- mail messages, and other
business records required for regulatory compliance
 Backup Considerations
• The amount of data loss and downtime that a
business can endure in terms of RPO and RTO
are the primary considerations in selecting
and implementing a specific backup strategy.
• The backup media type or backup target
• Granularity of backups
• File size and number of files
 Backup Granularity
• It depends on business needs and the
required RTO/RPO.
• Types :
– Full Backup
– Incremental Backup
– Cumulative Backup
 Recovery Considerations
• Retention Period
– Its is derived from RPO
– If the recovery point is older than the retention
period, it might not be possible to recover all the
data required.
– RTO relates to the time taken by the recovery
process.
 Backup Methods
• Hot backup - the application is up and running, with users accessing
their data during the backup process. This method of backup is also
referred to as an online backup.
• Cold backup - the application is not active or shutdown during the
backup process and is also called as offline backup
 A point-in-time (PIT) copy method is deployed in environments
where the impact of downtime from a cold backup or the
performance resulting from a hot backup is unacceptable.
 The PIT copy is created from the production volume and used as
the source for the backup. This reduces the impact on the
production volume.
 In a disaster recovery environment, bare-metal recovery (BMR)
refers to a backup in which all metadata, system information, and
application configurations are appropriately backed up for a full
system recovery.
Backup Architecture
Backup and Restore Operations

Backup Operations
Restore Operations
 Backup Topologies
Three basic topologies are used in a backup
environment:
• Direct attached backup
• LAN based backup, and
• SAN based backup.
• In a direct-attached backup, a backup device
is attached directly to the client. Only the
metadata is sent to the backup server through
the LAN. This configuration frees the LAN from
backup traffic.

Direct-attached backup topology

• In LAN-based backup, the clients, backup server, storage
node, and backup device are connected to the LAN. The data
to be backed up is transferred from the backup client (source),
to the backup device (destination) over the LAN, which may
affect network performance.

LAN-based backup topology

The SAN-based backup is also known as the
LAN-free backup. In this case the backup device
and clients are attached to the SAN.

SAN-based backup topology

Mixed backup topology
 Backup in NAS Environment
• Server based and Serverless Backup
 MODULE - 5

LOCAL REPLICATION
 Replication Terminology
• Source:Ahost accessingtheproductiondatafromoneormoreLUNson
thestoragearrayiscalledaproductionhost,andtheseLUNsareknownas source
LUNs (devices/volumes), production LUNs, or simply the source.

• Target:A LUN (or LUNs) on which the production data is replicated, is

called the target LUN or simply the target or replica.

• Point-in-Time (PIT) and continuous replica: Replicas can be either a PIT or

a continuous copy. The PIT replica is an identical image of the source at
some specific timestamp.

• Recoverability and restartability: Recoverability enables restoration of data

from the replicas to the source if data loss or corruption occurs.

• Restartability enables restarting business operations using the replicas.

The replica must be consistent with the source so that it is usable for both
recovery and restart operations.