VxVM root mirror

[Alan Shearer_1]

Hi,

I have no system to test this scenario on - just planning at the moment. So my question is if we use VxVM instead of LVM and create a root mirror. Do we still need to set hpux -lq in the AUTO file so the system can still boot if we lose a disk? - or is there no concept of quorum for a VxVM DG?

I've had a search around and can see no mention of it - making me think its not needed or that it's so obvious (except to me!) that it doesn't need mentioning.

Can someone confirm please?

[john123]

Hi Alan,

If am not wrong VXVM do not look for any quorum, And with VXVM the only switch avilable with 'hpux' command is to boot to veritas maintanance mode that is 'hpux -vm' which is something similar to LVMs LVM maintanance mode..

Regards
John

[Alan Shearer_1]

Thanks John.

Have you seen it in any docs I could check out? - I've looked at Admin, Concepts, Install, and Migration guides - but I'm sure I probably missed it somewhere.

May be there is a similar guide/how-to out there for creating a Veritas mirrored rootdg - with everything you need to make sure the system can boot from either disk, i.e. not just the commands to mirror the volumes.
- I know there are loads for LVM.

[Armin Kunaschik]

There is no -lq (or -lm) anymore if you use VxVM on your root disks. The only switch you (hopefully never) need is -vm (maintmode equal to -lm).

If you want to avoid licensing Mirror/UX and OnlineJFS, there is one other important thing: With BaseVxVM you are able to mirror only the standard volumes that are created in a default installation.
See http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=1041579 for detail.

There is another drawback: If a mirrored root disk crashes, the impact on the system is much higher than with LVM.
CPU utilisation is higher in such cases and it's harder to replace a disk compared to LVM. Don't try to reboot a system with a broken VxVM mirrored root disk! Most of the time this will fail and you need to manually remove the broken mirror in maintenance mode (-vm) using unfamiliar tools like vxmend etc.

My 2 cents,
Armin

[Paul McCleary]

Hi Armin,

I thought there was some limit on the number of volumes you could mirror, but I then read on the forum a few weeks ago that you could mirror any of the volumes in rootdg.

I read your post and it seems quite convincing that there is this limit of 8 named volumes that can be mirrored.

Out of interest do you know what the imapct is if you change the volume names from the defaults? Or what happens if when you build the system you have nine volumes - does it let you mirror the nine created at build time or still force you to eight?

Sorry Alan, I couldn't find much info on valid switches for VxVM other than the maintenance mode. I've very rarely used VxVM as boot disk and even then its been a boot from SAN so no mirroring.

Paul

[Armin Kunaschik]

As far I remember you cannot change the volume names. If you do they will not be mirrored.
I do clearly remember that the 9th volume will not be mirrored at all... you'll get an error message.
You can only work around this when you buy/install a full VxVM/VxFS license.

Ehm.. another BTW: With BaseVxVM/BaseVxFS you won't be able to increase filesystems while they are mounted.
If you feel confident with this, go ahead. Otherwise stay with LVM or buy a full license.

My 2 cents,
Armin

PS: Please assign points if you find answers useful!

[MikeL_4]

Procedure we use to move vg00 to Veritas control and mirror:

Bring alternate internal disk drive under Veritas control:
/etc/vx/bin/vxcp_lvmroot -v -b c?t?d?

Reboot server to newly created Veritas boot disk:
shutdown -ry now

Completely remove old lvm root disk , then mirror drives:
/etc/vx/bin/vxdestroy_lvmroot -v c?t?d?
/etc/vx/bin/vxrootmir -v -b c?t?d?

I've also attached a script we use to verify verify our primary and secondary boot devices are bootable...

[Alan Shearer_1]

Hi,

Thanks for the comments everyone, especially Armin.

Mike I did appreciate you taking the time to provide an answer, but converting from LVM to VxVM is not what I'm doing. This is starting using VxVM for everything, no LVM at all, right from the Ignite build.