On my last post, I mentioned about how easy it is to add or remove Oracle Automatic Storage Management (ASM) disks online.  But first, let’s discuss the reasons for doing so.  Why would you want to add or remove ASM disks?  Well, there are a few reasons that I could think of and they are:

  1. SAN migration – I purchased a new SAN for my current Oracle database since my existing SAN cannot handle the load any longer.  Also the new SAN is more cost effective and high performance.
  2. Performance – My database ASM disk group started out with only one disk for ease of management.  But now the load on the database has grown so I want to add more disks to the ASM disk group to take advantage of multiple disk queues at the operating system level for performance.
  3. Changing disk size – I started out with a single 1TB disk for my ASM disk group but now I would like to change that to 4 x 250GB disk for performance.

Adding and/or removing ASM disks can be done online.  However, I’d recommend doing this during low IO to the database so it can complete quicker.  When adding or removing ASM disks, the option “rebalance power” allows you to set so the rebalance can complete quicker.  The default is set to 1.  If your ASM disk group compatibility is set to 11.2.0.2 or higher, then the range is between 0 – 1024.  If the compatibility is set to lower than 11.2.0.2, then the range is between 0 – 11.  The higher the number, the quicker the rebalance operation and the higher the I/O overhead.

Now let’s add more disks to my current ASM DATADG disk group.

Notice that I have only one disk in my DATADG disk group.  I will create 3 more LUNs on my Nimble Storage array and present them to my database server.  I need to run iSCSI discovery/login and configure multipath for those 3 LUNs and then add them to my DATADG disk group.

Notice the existing disk highlighted in green was removed and has become a “FORMER” disk.  You can delete the disk by running the following commands:

Cleanup ASM disk header

[root@mktg04 ~]# /etc/init.d/oracleasm deletedisk DATA

Cleanup multipath

[root@mktg04 ~]# multipath –f /dev/mapper/<device>

Delete the disk from the SAN and cleanup iSCSI on the operating system.