topic Re: SAN file system sharing question in Operating System - Linux

SAN file system sharing question

avinash zodpe — Tue, 13 Apr 2010 11:53:05 GMT

All,
We are a Oracle ERP running business and are in process of upgrading our Linus from 4.4. to 5.4.
We have evrything on the HP MSA1500cs SAN.
Only OS is on the physical servers.

To avoid downtime, we have bought another server and have done a fresh install of 5.4
What we want to do now is
point this new server to same file system on the SAN accessed by one of our database server

Is it possible? Can we share the file system on the SAN?

thanks in advance
AZ

Re: SAN file system sharing question

Tim Nelson — Tue, 13 Apr 2010 12:46:42 GMT

Define share ?

You can present the storage to more than one server but you cannot register/use unless you have ocfs, gfs, or asm configured like in a cluster.

I would initially guess that the Oracle app versions would be different different enough between the two that you will have issues. ( this becomes a question for oracle support )

To be safe I would replicate the data test that way you do not corrupt anything and have a backout option.

Re: SAN file system sharing question

avinash zodpe — Tue, 13 Apr 2010 13:17:48 GMT

thanks for the quick reply.
I think I got my answer.

Re: SAN file system sharing question

Matti_Kurkela — Tue, 13 Apr 2010 13:26:52 GMT

Accessing a SAN-based filesystem simultaneously from two (or more) servers requires a special cluster filesystem, like GFS or OCFS.

Trying it with a standard ext3 filesystem will quickly cause massive filesystem and data corruption. Don't experiment with a production system.

What you *can* do, is make the downtime very short.

1.) Prepare the new system, verify that it sees the SAN disks. Don't add the SAN-based filesystems to /etc/fstab, don't run fsck on them and don't mount them at this time.

Backup /etc/fstab on the old server.

2.) Downtime begins. Shut down the applications on the old server. Unmount the SAN disks.

3.) Copy the lines referring to the SAN disks from the /etc/fstab file of the old server to the new server.

Comment out the same /etc/fstab lines on the old server, so that it won't try to mount the SAN disks automatically if it reboots for any reason.

4.) Mount the SAN filesystems on the new server, running a fsck if necessary.

5.) Start up application on the new server. Downtime ends.

6.) If the new server is stable, start tearing down the old server.

If it's necessary to roll back:

R1.) Shutdown the application, unmount the disks from the new server, and make sure it won't automatically mount them at reboot.

R2.) Restore the /etc/fstab on the old server that was backed up in step 1.

R3.) Restart application on the old server.

MK

Re: SAN file system sharing question

avinash zodpe — Tue, 13 Apr 2010 14:10:04 GMT

thank you very much for detailed explaination. That really helps !!!

Re: SAN file system sharing question

Steven E. Protter — Tue, 13 Apr 2010 14:12:16 GMT

Shalom AZ,

You can make disk on the SAN visible to more than one system at the same time, but not mount or start Oracle.

Once you are finished installing Oracle on the new server, a short cut over can be arranged. Downtime should be limited to how long it takes to stop oracle on one system and start it on the second.

SEP