topic root mirror fall back in Operating System - HP-UX

root mirror fall back

Pradep — Mon, 06 Oct 2008 13:53:21 GMT

Hi,

i am patching my server, which has root mirror.
if patching goes bad, i want to boot from alternate mirror disk and copy it to primary disk to make the server in old state.
can u guide me to a doc which clearly exlains how to do it.

thanks,
pradep

Re: root mirror fall back

Torsten. — Mon, 06 Oct 2008 13:57:50 GMT

If you write to a mirrored LV, data will be written to all mirrors.

So if you patch your system, patches will be written to both disks.

Your possibilities:

1) create an ignite backup
2) use DRD - dynamic root disk
3) shutdown the server, remove 1 disk, boot up (using -lq option) and install.

If this goes wrong, shutdown and use the other disk - take care, remove the disk with the "bad data" first.

IMHO you should always create an ignite backup, no matter what you do next (2 or 3).

Re: root mirror fall back

Ganesan R — Mon, 06 Oct 2008 14:33:32 GMT

Hi,

Easiest way is to take ignite backup and patch. If things went wrong after patching then restore from ignite.

Other way is, If you have physical access to the server remove the mirror disk physically(not LVM break). Boot from primary disk. Patch the server. Everything is ok put back and sync. If things went wrong boot from alternate and sync to primary.

There is a way to break the mirror online and patch then remirror. But that is tedious job.

Re: root mirror fall back

Pradep — Mon, 06 Oct 2008 22:01:25 GMT

thanks. But how to sync secondary disk to primary ? becuase if the boot from sec., when pri also connected, pri ( with bad data) will overwirte to sec ( with good data).

Re: root mirror fall back

Mridul Shrivastava — Mon, 06 Oct 2008 23:02:01 GMT

Remove the primary and insert seconday. Boot using secondary disabling quorum mode.
Once system boots from secondary. Insert back the primary and do a resync. That will be done from secondary to Primary.

Re: root mirror fall back

Doug O'Leary — Mon, 06 Oct 2008 23:29:59 GMT

Hey;

A few people have actually given the right anawer already. While possible, it's not really practical to protect a root mirror then resilver the mirror if the patching goes bad.

The right answer is the make_net_recovery or make_tape_recovery that comes with the (free) ignite software. You can recover a system to full operational status inside of 45 minutes. That 45 minutes is a lot cheaper in terms of time, energy, potential issues than would be the tear the alternate root disk out of the system approach.

HTH;

Doug O'Leary

Re: root mirror fall back

Pradep — Tue, 07 Oct 2008 07:47:20 GMT

Hi,

when i am booting from Pri in -lq mode. and inserted sec disk, the isocan says disks claimed, but sync is not starting. and pvdisplay says pvchange: Couldn't query physical volume "/dev/dsk/c3t6d0":
The specified path does not correspond to physical volume attached to
this volume group.

what should be the command sequence to do it ?

Re: root mirror fall back

Duncan Edmonstone — Tue, 07 Oct 2008 09:09:29 GMT

paradep,

where are you up to? It reads like you've succesfully done the patching and now want to sync the removed disk back with the primary?

Is that the case? If so and you've re-inserted the 2nd disk and proved you can read from it by doing a diskinfo or using dd, then you should just be able to run:

vgchange -a y vg00

To bring the disk back in and sync now, or:

vgchange -a y -s vg00

to bring the disk back in followed by:

lvsync /dev/vg00/lvol1
lvsync /dev/vg00/lvol2

etc.

to resync your LVs at your leisure.

HTH

Duncan

Re: root mirror fall back

Pradep — Thu, 16 Oct 2008 05:07:40 GMT

Thanks you ..Tested the fall back scenario. works great !!