Mirroring data from local to SAN storage

[David Cassin]

I have a server with local storage under LVM that i want to migrate onto SAN storage.

Can I do:
1. vgextend the volumes with the SAN disks as alternate links
2. vgsync the volume
3. vgreduce the volumes of the local disks (effectively splitting the mirror)

Can this all be done while the server is up and running? Is there a better way to do this while the server is on-line?

[Steven E. Protter]

Might work.

I might try:

lvextend -m 1

mirror is created.

lvreduce or split the mirror to remove the local logical volume.

Just a thought.

SEP

[Victor BERRIDGE]

Hi David,

1) Yes but dont get confused the san disky are NOT alternate links..

Can this all be done while the server is up and running?
You have no other choice with this solution except stopping the applications...
Is there a better way to do this while the server is on-line?
I tried by cpio... if the applications or RDBMS are up this is the only possible alternative to be synchronized
I did it once a few years ago, it works well but be aware of overhead and time - so choose the right moment....


All the best
Victor

[Mel Burslan]

Yes it can be done. We have used this approach migrating our data from an old EMC array onto XP1024 last year around this time. The only concern is, if your Fibre Channel adapters connecting your server to SAN is being used for some other purpose, like a backup library link. If so, that oparation will be heavily impacted.

Also, there will be some cpu and i/o performance degradation to be observed while the data transfer is in progress. Otherwise, the method is proven working.

[Robin T. Slotten]

Yes, I have done this from JBOD to 12H Autoraids; from the Autoraids to a XioTech SAN; and recently from the XioTech to an EVA 5000 array. As others have cautioned, You can impact performance while the mirror is being Sync'ed, but it is an effective way to keep the database up. Test this on a non critical volume as not all SAN arrays approve of this method. I have never had a problem, but procede with caution.
Rob...

[Jeff Schussele]

Hi David,

Yes this can be done & is frequently employed to do exactly what you're trying to accomplish - move off local to SAN storage.
One caution I would give you is to size the LUNs on the array as closely to the size of the local disks as possible. The reason being that in a mirror situation you are limited to the size of the smallest PV in play. So if you have 9GB disks & the LUNs are 18GB, you'll essentially be wasting 9GB of the LUN.
The only way around that is to backup the VG, destroy it & restore the data to the newly created VG using the LUNs.

HTH,
Jeff

[Devender Khatana]

Hi,

Yes it can be done online but will affect performance so do it at a time when utilization is quite low. Another good point what Jeff raised is to check what will be the max. size of PV's (LUNs) supported in your existing VG's.
Find this be "vgdisplay -v /dev/vgname" command. The multiplication odf two parameters PE Size & MAX PE Per PV will give you this size. If this is less then you new LUN's you will not be using full size of your new LUNs after extending VG's to new LUNs.

HTH,
Devender

[David Cassin]

Thankyou all for your responses, i'll definately be using the info, and testing before updating live data.

[David Cassin]

Thread closed, as per previous update.

Thanks.