Migrating data from one SAN to another SAN Storage

[d_allen111]

Hi folks,

I've been a long time reader, but this is my very first posting on this great website.

I have been reading and gathering info regarding to data migration from one SAN to SAN Storage. However, I do still have a few questions about Linux and LVM LUNs and such.

Let's say at this point, we don't have to worry about the SAN Fibre switches and multi-pathing between the hosts and our one and only SAN storage array.

What we have is the old Hitachi 9000's series SAN array and we're in the process adding a new HP EVA 4400 series SAN Storage array. We're going to move a few hosts from the Hitachi SAN storage to the new EVA4400 permanently. Once the data are moved, I will than umount the old logical volumes then.

Each host currently has two (2) Volume Groups and four (4) Logical Volumes. We're currently using LVM2 on the host side.

What I will do is to add this new SAN "EVA 4400" to Fabric A & B with a new zone and create the Volume Groups with the same amount of Logical Volumes. Once all that and done, I will mount the new mount point to the hosts (hopefully I don't have to reboot since I am using Fibreutils).

My questions are:
1. Should I use Backup & Restore procedure technique?
2. Should I be using LVM Snapshot technique?
3. Should I be using rsync technique here?

What other method should I be using for this migration project??

I am not an expert at Storage or Redhat 'RHAS 4.0' Linux, but I feel very comfortable working with the Hitachi and EVA 4400 SAN Storage.

I am also looking for best advice and best practices. I do appreciate all the help I can get and hope for some day I can return the favor.

Regards,

David A.

[IBaltay · Accepted solution]

Hi,
the LVM mirror idea seems to be the best idea here (if available in RHAS 4.0 release):
1. New EVA LUNs VGs addition
2. Hitachi and EVA LUNs mirror.
3. Hitachi mirror reduction


links:
http://www.guug.de/lokal/rhein-main/2004-09-23/LVM2_sage_23.09.pdf

http://devresources.linux-foundation.org/dev/clusters/docs/cluster_summit_mirror_paper.pdf

[d_allen111]

Hello IBaltay:

Exellent documentation and thank you!!

David

[Patrick Terlisten]

Hello David,

I often use host-based mirror for such operations. Take a look at the software-raid features of your distribution.

Best regards,
Patrick

[d_allen111]

Hello Patrick,

Where would I be able to find more info on Software Raid for Redhat Linux 4.0?

Thank you very much for your advice.

David

[Patrick Terlisten]

Hello,

check the documentation of dmraid. Take a look if it's already installed on you machine.

Best regards,
Patrick

[d_allen111]

Thanks, Patrick!

I went through the document on my Linux server (man dmraid) and to find that I need more info on dmraid. Is there another place like "How-to" or "Best Practices" for dmraid?

Again, many thanks!!

David A.

[TTr]

Check out the man page for the pvmove command in Linux. If it is the same as in HP-UX, you can use it very easily. You have to make the old and new disk LUNs part of the same volume group and with pvmove you can move the extends from one disk device to another. You can use pvmove live, no downtime and no mirroring is needed.

PS. Although you are very prompt to thank every individual response, in these forums, this is how you say thanks: http://forums11.itrc.hp.com/service/forums/helptips.do?#34

[d_allen111]

Hello TTr!

Well, looks like Linux (RHAS 4.0) does use pvmove as you've suggested. Is there more in-depth info on this subject, so that I can read more into this??

Thank you.

David A.

[TTr]

I am not a Linux admin but I have used it a lot on HP-UX and it works extremely well. You issue the command to move a specific logical volume only or move a whole physical volume to a new one. You can monitor its progress by running lvdisplay repeatedly. As the extends are moved you see them in the pvdisplay listing. The LEs that were moved already have their PEs on the new disk and the ones that were not moved have their PEs on the old disk. The LE that is being moved at that time shows up with both PEs, one PE on the old disk (current) and one on the new disk (stale). When the copying is finished, the PE on the old disk is deleted and the PE on the new disk becomes current.

Search for "pvmove" in your favorite Linux websites to find any references.

The HP-UX man page: http://docs.hp.com/en/B2355-90692/pvmove.1M.html

Also check out these documents
http://docs.hp.com/en/5992-4589/ch03s04.html

This one covers a special case where the new disks are much bigger that the old ones and not the entire new space can be used in LVM because of extend number limitations. I don't know if this applies to Linux of to your case. If your new disks are not much bigger than the old ones ignore vgmodify but look at the pvmove examples in http://docs.hp.com/en/vgmodify/vgmodify_wp_modified_final.pdf

[d_allen111]

Thank you!!

David