LVM changes between ignite backups

[Tim Medford]

Hi All,

I don't have a problem at this time, but I just wanted to get some steps documented in our DR recovery guide.

Suppose we take an ignite tape backup on the 1st of each month. Then throughout the month a couple LVs are entended, maybe a physical volume is added to a VG. These LVM structures are stored on an EVA accessed via fibre channel.

If during the last week of the month we lose the root drive and restore from the Ignite created on the 1st, what happens to those LVM structures? Will they reflect the increased size, or will they be the original size recorded on the ignite tape on the 1st?

I guess I'm just not sure where all that info is stored. Is it in the LVM headers on the EVA itself, or is it on the root drive?

Thanks in advance,
Tim

[Tim Nelson]

Recovering from ignite is just like reinstalling the server from scratch with the exception that all your configs including fs sizes are included in the ignite image from the point in time that the image was taken.

If you make changes after you take an image and then use a previous image to recover you will get the configs from the date of recovery, NOT any changes after the image was created. All lvm structures are recreated from the image.

[James R. Ferguson]

Hi Tim:

LVM headers are stored on the physical disk defining them. Changes are, of course, recorded by default in the files in the '/etc/lvmconf' directory on vg00.

In disaster recovery tests I do, I Ignite vg00 and using template scripts, I re-create my current non-vg00 LVM disks into which backup software then loads their data.

If you lost your root drive (and its mirror? --- you do mirror, I hope) and you had to resort to a re-Ignite (of vg00) I expect that you would 'vgimport' your non-vg00 volume groups. At that point, I would *manuallly* do 'vgcfgbackup's of the newly imported volume groups to update your '/etc/lvmconf' directory with current LVM metadata.

Regards!

...JRF...

[Tim Medford]

Thanks for the info.

James, I think what you said is similar to what I was thinking too.

I would be able to do as you suggest:

1) restore vg00 from ignite
2) recreate the non-vg00 structures from scratch using scripts
3) restore data from tape.

To save time though, and in a best case scenario, the data on the EVA is intact and would not need to be restored from tape. Assuming all the hardware paths remain constant I should be able to restore vg00 and the other data will just be there. At a minimum though, I'd have to vgimport to get the new size information and rebuild /etc/lvmconf?

We do mirror in the sense that our root drive is a RAID-6 device, a P400 controller on an rx3600 server. We can lose 2 drives, plus there's a hot spare configured.

Thanks for your thoughts.

[Tim Nelson]

Kudos to JRF for reading the question correctly (again ;).

Yes your non-vg00 LVM structures will stay intact. A vgimport may not even be needed after an ignite recovery as long as the storage nor its device paths have changed.

( I read this as changes to vg00 which is clearly not what your question asked )

[James R. Ferguson · Accepted solution]

Hi (again) tim:

> Assuming all the hardware paths remain constant I should be able to restore vg00 and the other data will just be there.

Essentially, yes. Mind you, the hardware paths (before 11.31) might change when you Ignite, particularly if you have added and/or deleted hardware since the last ignition. This isn't an issue. You can always use 'vgscan -p -v' to "see" what disks belong to what volume groups. Using this output, you can specify the devices for your 'vgimport' without effort.

Regards!

...JRF...