Reasons to Use ASM on NFS

My tweet from a few days ago: “Personally I don’t see the point building ASM on (d)NFS. ASM suppose to exclude unnecessary layers. In NAS case it adds an additional layer.”

Since then, Oracle people in my Social Media environment have helped me find several legitimate reasons to run ASM on NAS. Thank you folks very much. Now I am sharing our common thoughts with the rest of the community.

Oracle Support

The very first question you will ask is: Does Oracle support putting ASM disks (devices) on NAS?
And the answer is : YES it (surprisingly) does.
Check this out:
Oracle® Database Installation Guide 11g Release 2 (11.2) for Linux Part Number E24321-07
Creating Files on a NAS Device for Use with Oracle Automatic Storage Management.
From that point, the question is not “can we?”. The question is “why?”

Reasons for using ASM on NFS

The following is what we have noted as of now:

• The license restrictions for Standard Edition. You can use RAC for Free if you follow license restrictions. One of them is to use ASM. If you would like to use NAS as a storage at the same time, you have no other choice but to use ASM on NFS.
• ASM striping between filers. As simple as it gets. You can use ASM to mirror your data across different storage units. I know, I know. You can do it using NAS vendors’ features. But who knows, maybe someone can’t because of licences or other implications. BTW: This option is valid for any Storage (e.g. SAN).
• “0” downtime migration from one storage to another. If you use ASM as opposite to datafiles located directly on NFS, you could use ASM rebalancing across ASM disks located on different storage units to migrate your database with zero downtime. You will need ~5 minutes downtime in the case of files located directly on NFS.
• RAC on NAS. We need at least one ASM disk group to be created for OCR and voting disks.
  • Correction (thanks to Leighton L. Nelson): If you want to run RAC on NAS you can use either ASM or kNFS.
  • Ref: Overview of Oracle Clusterware and Oracle RAC Storage Options from Oracle® Grid Infrastructure Installation Guide 11g Release 2 (11.2) for Linux Part Number E22489-08

Please feel free to comment, especially if you know other reasons for creating ASM on NFS or see any mistake in my blog post.

Yury