TECHNICAL BULLETIN / COFFEE BREAK

COMPARING ISCSI
INITIATOR IMPLEMENTATIONS

WHAT’S ALL THE BUZZ ABOUT ISCSI?

With the advent of iSCSI as the standard for networked storage, businesses
can utilize existing skills and network infrastructure to create Ethernet-based
SANs that can deliver the performance of Fibre Channel—but at a fraction of the
cost. iSCSI is designed to enable block-level data to be transported between a
server and a storage device over an IP network. An iSCSI initiator is hardware
or software that runs on a host and initiates I/O to an iSCSI target, which is a
storage device that responds to read/write requests.
When creating a connection, an iSCSI initiator and iSCSI target
authenticate each other. After login, the target is seen as a There are three basic types of iSCSI
local device that can be used like any other SCSI disk. initiators:
CHOICES, CHOICES • Software-based iSCSI driver with a
standard network card.
To access storage in an iSCSI SAN, a host only needs an iSCSI
• Software-based iSCSI driver with a
initiator and a network connection. Initiator implementations
differ in price, performance, and flexibility: network card that incorporates a TOE to
reduce the TCP processing load on the
• Software-based iSCSI driver with a standard network card.
host’s CPU.
All iSCSI and TCP processing occurs in the host’s CPU.
• Host bus adapter that offloads both TCP
Many operating systems provide software initiators as a
standard feature, minimizing costs. and iSCSI processing.

• Software-based iSCSI driver with a network card that

incorporates a TCP offload engine (TOE) to reduce the TCP
processing load on the host’s CPU. Many server network
interface cards (NICs) include some level of TCP offload.
• Host bus adapter that offloads both TCP and iSCSI processing. This type of
initiator reduces both the TCP and iSCSI processing load on the host’s CPU.
Some iSCSI HBAs can be used for both iSCSI and standard network traffic,
while others require a separate port for non-iSCSI traffic.

INCREASING HOST CONNECTIVITY TO TARGETS

T The same solutions that increase network connectivity on
a host provide highly-available access to iSCSI targets. Host
connectivity can easily scale upwards using hardware or
software-based methods, including multi-homing, teaming,
or multipath I/O.
• Host multi-homing using NIC/TOEs can provide some
failover and load balancing capabilities.
 • Teaming homogeneous NIC/TOEs can provide both failover and load balancing capabilities; however,
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special setup is required.
• Host-based MPIO can provide the best failover and load balancing capabilities and supports a broad
range of network cards and HBAs.

Major operating systems support iSCSI initiators. With dynamic discovery

methods, high performance offload engines, and scalable host connectivity,
iSCSI is able to provide a cost-effective solution for simplifying and managing
networked storage.

ACCESSING TARGETS FROM HOSTS BOOTING SERVERS FROM THE SAN

iSCSI is the only storage networking protocol iSCSI initiators can support booting servers directly
to support authentication, authorization, and from the SAN. These servers may be diskless
encryption in the protocol standard. This typically systems, with all data on the SAN, or may include
results in security that is well integrated and a local disk for swap areas. Booting requires BIOS
easy to use. iSCSI initiators support manual and support – either in the server BIOS, or in the NIC/
automatic methods for connecting to iSCSI TOE/HBA BIOS. This can allow servers to be easily
targets. All initiators support the static procedure, interchangeable, and stateless — a server can be
in which an administrator manually specifies the provisioned to another application/service by
full target iSCSI name and IP address (portal). changing its boot parameters.
However, to simplify the connection process,
most initiators support discovery, which is based ISCSI — THE BEST SAN SOLUTION
on the SendTarget command. Using discovery, an AVAILABLE TODAY
administrator specifies just the portal address. Only With capabilities for booting and discovery—in
targets authorized for the initiator are returned and addition to data access — iSCSI represents one
made available for access. of the most comprehensive storage protocols
available. Major operating systems support iSCSI
DYNAMICALLY MANAGING TARGETS AND initiators, providing businesses with a range of
INITIATORS implementations and features. With dynamic
Internet Storage Name Service (iSNS) can be discovery methods, high performance offload
used to facilitate the discovery, management, engines, and scalable host connectivity, iSCSI is able
and configuration of iSCSI devices. Instead of an to provide a cost-effective solution for simplifying
administrator having to constantly configure and and managing networked storage.
reconfigure individual storage devices, an iSNS
server dynamically handles device discovery and
authentication services. Targets register properties
and access controls with the iSNS server. Upon
querying the server, initiators are shown only the
targets for which they have authorization. iSNS
servers can also provide zoning and login control
services and state change notification. In addition,
an iSNS server emulates Fibre Channel fabric
services, so it can provide a simple method of
interoperation (using iFCP gateways) between IP
and Fibre Channel networks.

© 2008 Dell Inc.

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