DEV Community

technonotes-hacker
technonotes-hacker

Posted on

Promotion - Oracle ASM

#architecture #database #infrastructure
  • Oracle Automatic Storage Management (ASM) is a built-in volume manager and file system for Oracle Databases that simplifies storage administration.
  • Its a Volume Manager
  • What will the Volume Manager will do ? and what do you mean by Volume ? 
5TB Big Data , you need to store this --> In storage every single disc is having only 1TB. 
5 Hard Disc Needed. 
Multiple Disc into single disc to the outside world.
1 Volume can have 1 Physical Hard Disc or Multiple Hard Disc.
Enter fullscreen mode Exit fullscreen mode
  • These storage software will take care the Volume Manager also.
  • If we assign Multiple disc to ASM , ASM can handle the disc , ASM add the disc from the Volume , Remove the disc from the volume , ASM can perform the redundancy of the storage, ASM can perform the Load Balancing inside the disc.
  • ASM provides the Volume Manager layer which is needed by every storage software.
  • ASM also acts as a File System.

What you mean by File System ?

  • Its a storage area.
  • File System is basically a STORAGE.
  • File System as Storage area for Oracle Database.

Oracle Clusterware

  • You can use it for Cluster Management not only for Oracle but for any other infrastructure.
  • It can be installed to manage the cluster , it doesnt mean that you need to have only Oracle RAC.

Oracle ASM --> its is File System Storage only for Oracle RAC / Standalone Database. Its not supported for others.

What type of File can store in ASM ?

  • RMAN Backup
  • Flash Back Log
  • Export Import Files
  • Expect PFILE , all are in Binary Mode. So all files can be stored in ASM.

DiskGroups in ASM

  • Collection of disks which make a volume ( diskgroups )
  • Diskgroup is nothing but Volume.
  • Diskgroups --> Collection of disk at the OS level.
  • You can assign / must assign a name to diskgroup. Eg., ASM1 /dev/sdc1 --> The ASM1 name will be assiged to the physical disc.
  • Minimum ASM Structure defined by Oracle is --> 3 Discgroups for basic Oracle RAC configuration.
  1. CRS Diskgroups --> To store cluster related files
  2. DATA Diskgroups --> To store database files like datafiles etc
  3. FRA Diskgroups --> To store FRA files

FRA --> Fast Recovery Area

Where we named ASM1 ? At what place ?

  • When we installed the ASM Binary , Post ASM binary , we had issued a command " Oracle ASM CREATE DISC ".

What is DISkS ?

  • Physical HDD Storage
  • One HDD can't belong to two discgroups
  • But Multiple HDD can be belonged to one single discgroup.
  • Types of storage considered for ASM:
  1. Complete HDD partition.
  2. Multiple HDD Partitions assigned to single ASM disks
  3. NFS
  4. LUNs allocated from Storage. Oracle doesn't recommend this ? Why ?
  • ASM is already a Volume Manager, so when allocate LUNs from the storage server , storage software is again a Volume Manager. Two Volume Manager are not recommended for storage of data. Because you will have Redundancy of Volume Manager.

Eg., for point 2

/dev/sdc
/dev/sdc1 --> ASM2 ( These are only disk )
/dev/sdc2 --> ASM3
/dev/sdc8 --> ASM7

ASM2 is a single disk , can be assigned to one diskgroup. But ASM2 can't be assigned to Multiple Diskgroups.

  • 1 single diskgroup can have multiple disk , it means , single diskgroup can have ASM2 , ASM3 .
  • For ASM1 , I can add --> ASM1 /dev/sdc1 + /dev/sdd1 + ..
  • These disk will have datafile.

Lets get inside the ASM Instance

What is Oracle ASM Instance on STANDALONE DATABASE?

  • Its built on same technology as of database instance.
  • SGA + BG Processes ( BackGround )
  • No Redo Logs
  • Its just a mediator between Oracle Instance and the Storage Disc.
  • Its very small when compared to Oracle Database Instance as it performs very small task.
  • Its smaller in size when compared to DB instance.
  • where is Oracle ASM installed ? Oracle ASM is installed in GRID_HOME. ASM binary are installed under GRID HOME.
  • What exactly stored ? what is the metadata inside the ASM ? --> ASM manages the exact metadata of the disk group and provide file layout to Oracle Instance.
  • ASM instance is like a mediator between Storage ( diskgroup ) and Oracle Instance.
  • Every single machine as one ASM instance running on it.
  • 3 DB instance on a single machine ==> 1 ASM instance shared by all the DB instances.

What is Oracle ASM Instance on RAC DATABASE?

  • Every single machine / node has one ASM instance running on it.

Oracle ASM Instance Failure

  • If the Oracle ASM fails on one node --> what will happen ? --> what happens to the Oracle DB instance ? or If the Oracle Database is running and suddenly Datafiles are deleted , what will happen ? DB instance FAILS. Same DB Instance also fails if ASM fails. ( DB instance will also FAIL )
  • Can I stop the ASM instance when DB is up and running ? ( Important Interview Question ) ---> Stop all the DBs instance accessing the ASM before stopping the ASM instances. This is the procedure.
  • From 12c RAC --> ASM Instance Fail over was introduced --> Oracle ASM Flex Cluster , need to be enabled.
  • what the ASM flex Cluster will do ? --> If the ASM in node 1 fails , then it communicates to ASM in node 2 and then access the shared location.

  • This is only available only from Oracle RAC 12c.
  • This is like High Availability.

ASM Mirroring & Failure Group

  • Mirroring is like Maintaining a copy of your data.
  • Its like "A diskgroup is mirrored to another diskgroup".
  • Oracle ASM itself provides the redunduncy.
  • You have to mention the redundancy at the time of disk group creation.
  • Once done , it can't be changed.
  • Types of Redundancy in ASM :
  1. Normal --> 2 way redundancy --> 2 failure groups , Max you can have 3 Failure groups.
  2. High --> 3 way redundancy --> 3 failure groups , Max you can have 5 Failure groups.
  3. External --> No ASM level redundancy or you can have external Softwares for redundancy.

What is Failure Groups ?

  • One Single Failure Group is one Single redundant Copy.
  • To increase the redundancy , we can have multiple Failure groups.

  • Failure Group are defined while creating the disk group.
  • Failure Group is nothing but the redunduncy , no of failure group is nothing but the level of redunduncy.

ASM Adminstrator

  • ASM needs the Utility to administor.
  • SQLPLus ( How ? because ASM instance is like Oracle DB instance , so SQLPlus can be used )
  • ASMCMD --> ASM command mode
  • ASMCA --> ASM configuration ASSISTANCE --> its like GUI ( All things can be performed , even the upgrade of ASM ).
  • These are the Utility used. But these are only for STANDALONE DB.
  • What about RAC based Oracle Instance ? For Multiple ASM , then SRVCTL --> Clusterware Level Utility which allows you to administer all ASM Resources.

Note

  • DiskGroups as Table space
  • Disks --> is a Datafile.
  • In a tablespace can have multiple datafile. But single datafile can't be assigned to two tablespace.
  • SGA --> System Global Area
  • CRS --> Cluster Ready Services
  • LUNs --> Logical Unit Numbers
  • Database backup is taken by RMAN. ASM will allocate the channel to the diskgroup. No ASM comes inbetween for backup . RMAN directly write into the ASM diskgroup. No over head on the ASM instance.
  • When you take RMAN backup for OS level disk , does it give over head to the OS system ? Not really . Same , if you allocate channels to ASM diskgroup , RMAN will continur to write and ASM instance continue to perform until the diskgroup is full or ...
  • If you talk about Volume Manager --> Stripping , Mirroring , Load Balancing --> Everything is supported by Oracle ASM.
  • Irrespect of Database instance in a single node , only one ASM will be running for each node. That is the benefit .
  • Mostly EXTERNAL will be configured , as they will allow the storage team at HARD DISK level.
  • SRVCTL --> Server Control

Top comments (0)