Exploring ASMLIB

What is Oracle ASM?

Oracle Automatic Storage Management (ASM) is a storage management solution. It consists of logically group disks, known as volumes or diskgroups, it holds database files.

What are benefits of ASM?

• It lets you add/remove disk without downtime by automatically redistributing disk contents.
• ASM provides uniform performance by spreading file content evenly on disks.
• Fault tolerance can be achived by ASM 2-way or 3-way mirroring
• Flexibilty to use storage management options provided by storage vendors.
• Easier storage management for DBAs 

What is ASMLIB 

ASMLIB is an Oracle kernel driver or library to enable ASM I/O in Linux for various disk type (IDE, SCSI, RAID, Multipath) providing better I/O performance by eliminating UNIX I/O API. ASMLIB provides interface between Linux operating system and database ASM devices. In database 12c, ASM Filter Driver is recommended in place of ASMLIB 

How to setup ASMLIB support? 

On Linux servers:

1. Download ASMLIB from OTN
2. Install set of RPMS (oracleasm) on Linux
3. Create mount point /dev/oracleasm with

/etc/init.d/oracleasm configure 

4. Setup proper owner(UID), group(GID) and permission on devices
5. Make disk available by running oracleasm createdisk 
6. Verify installation and make sure disks are visible on all RAC nodes 

/etc/init.d/oracleasm status  

Checking if ASM is loaded:  [  OK  ]
Checking if /dev/oracleasm is mounted: [  OK  ] 

List usable marked disks

oracleasm listdisks 

Query ASM library in use

SQL> select library, path from v$asm_disk; 

7. Set ASM init.ora parameter for asm_diskstring 
8. Startup ASM instance(s)