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RE: SAN migration question

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Adam Noble
Super Advisor

RE: SAN migration question

Hi all,

We are migrating to a new SAN the vendor will be carrying out a disk copy at the array level for us. I have been reading a number of old threads which seem to suggest you have to vgexport the old VG's and therefore remove device files. In honesty I don't understand why that is the case. The disk headers will be identical so surely when it scans the disk on reboot the new volumes will simply be imported. I will do a -p to take a copy of the files without actually exporting for a backup but do I really need to remove them.

The intention is to shut down the hosts do a cold copy at the array level and then zone in the servers to the new array and reboot. Sounds far too easy and sure your going to tell me that it is not!!!
6 REPLIES
Adam Noble
Super Advisor

Re: RE: SAN migration question

Just realised I was a little naieve the disk names will more than likely change so I do need to vgexport.
Mel Burslan
Honored Contributor
Solution

Re: RE: SAN migration question

Holistically looking at your picture

NOTE LVM VG and PV are all at logical volume manager (LVM) level references below

You have LVMs living on VGs
You have VGs living on PVs
You have PVs living on physical spindles
Your spindles are on a SAN array

You move exchange your SAN frame
Your spindles changed.
Your LVM PVs know your old spindles and how to talk to those. Unfortunately at this point, the game has changed. Your server LVM needs to be reacquainted with the spindles, even if the LVM headers are the same, it still needs to learn how to talk to the hardware for the lack of better terminology.

This is where vgexporting (with map files) from old volumes and vgimporting once you are on the new volumes come into action. My terms may not be accurate but short of a miracle, I don't think you can just bitcopy the data from a SAN fram to a different manufacturer SAN and be able to read it without any additional efforts.
________________________________
UNIX because I majored in cryptology...
Ismail Azad
Esteemed Contributor

Re: RE: SAN migration question

Hello Adam,

> Sounds far too easy and sure your going to tell me that it is not!!!


Well adam, if you want to migrate one set of disks to another set of disks with LVM v2.x it's way more easier than this . There is a very nice command called as vgmove which allows you to do this making migration much more simpler which could be one of the reasons to go LVM v2. Well whatever you have mentioned in the post looks like standard procedure at the O.S level as far as LVM is concerned.

You need to present what is called as a diskmap file which is textbook documentation naming which would allow you to specify the set of disks that you want to migrate in terms of device files.

And what is way cooler is that you tend to keep the high availability aspect as this requires absolutely no_downtime.

Regards
Ismail Azad




Read, read and read... Then read again until you read "between the lines".....
Wilfred Chau_1
Respected Contributor

Re: RE: SAN migration question

I suggest you use the -s flag (with -m and -p flag) to create a map file for all VGs for your SAN migration.

The -s flag will scan the header of the disks and put the VGID in beginning of the map file.

The vgimport will then use the vgid to import the proper disks into the vg.
klb
Valued Contributor

Re: RE: SAN migration question



I vote vgexport/vgimport ( with detailed mapping ).

However, you are still going to have to figure a way to verify all those LVM objects and their contents after the migration to the new SAN is complete.

My concern would be that some time after your migration, your applications stumble upon some bit of corruption on disk ( logical corruption resulting from the SAN to SAN level copy ) and fail. At this point, even your backups could be corrupted, depending on the amount of time that has passed, which could leave you in a really bad spot.

Spend some time planning out your post migration activities and decide just how thorough you want to be.

Hth,

-klb
RajuD
Frequent Advisor

Re: RE: SAN migration question

Hi,

We have done san migration in cluster environment plz find the procedure attached which we have followed
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