Chances of getting data back due to LVM/VxVM disk failure

[Srikanth Arunachalam]

Hi,

Can someone tell me what is the chances of recovering data due to disk corruption due to LVM/VXVM. We have too many disks and quiet lot of mount point in our applications. Before creating the mount points for VxVM for the first time in the system. I would like to confirm the chances of restoration of data after disk gets corrupted and system crashes due to VxVM problems. What precation I need to take for my system with the below configuration ?
OS : HP-UX 11.23
Root disk is mounted on LVM with VxFS.
Application disk is mounted on VxVM with VxFS.
Application consists of vital oracle data and we nearly have 30 mount points for our application.
The application is running in MC serviceguard cluster with Oracle dataguard replicated to remote system.

[Pete Randall]

Your chances of recovery increase in proportion to the thoroughness of your backup plan. No backup plan = no recovery. Good, thorough backup plan = good chance of recovery.

For your root disk, I would suggest using Ignite:

http://www.docs.hp.com/en/IUX/

For your other data, use a conventional backup tool.


Pete

[A. Clay Stephenson]

It depends. If you mirror each logical volume then the probability of recovery is very nearly 1.0; if you don't the probability is very near 0.0. NEVER assume that mirroring takes the place of backups.

In general, assuming that you are mirrored, it is far more likely that the real data loss will occur as a result of some human action (e.g. rm -r, creating a filesystem on an "unused" disk, application errors, etc.) If you are mirrored and use only hot-pluggable disks then you even need to shutdown to replace a disk and your users will never even know a disk has failed. I have not shutdown to replace a failed disk in 7-8 years and over that period I have replaced hundreds of disks.

[Rick Garland]

You got a backup - you can recover
No backup - no recover

Even though you may have dataguard or snapcopies somewhere else, this does not replace the need for backups.

[Srikanth Arunachalam]

Thanks Pete. Backup was one such thing I missed in my last mail.
We have RMAN backup for Oracle and we take system backup overnight everyday.

To add to my last question, I do need to take backup of LVM using vgcfgbackup and dgcfgbackup that I understand. After performing restoration of these utilitites, will I be safely able to recover data from disk. Are the actual data in the disk safe due to any logical volume corruption and after applying restoration as well.

[James R. Ferguson]

Hi:

By default, 'vgcfgbackup' is run automatically anytime LVM changes are made.

This is a backup of only the LVM configuration of a volume group and as such is used principally during disk replacement in order to write the LVM header information onto a replaced disk. This is not a backup of any user data on the disk.

By default, the '/etc/lvmconf' directory is the target directory for the volume group information.

Regards!

...JRF...

[A. Clay Stephenson]

vgcfgbackup and vgcfgrestore do not backup and restore actual data but only LVM metatdata. Essentially, these utilities allow you to replace a failed disk by restored disk layout metadata but they do absolutely nothing about the user data itself. Indeed, they wouldn't even know (or care) if a particular LVOL even had a filesystem on it. However, vgcfgrestore when combined with mirrored LVOL's does allow you to replace a failed disk (even a boot disk) "on the fly" and the applications will not miss a beat.

[Srikanth Arunachalam]

Thanks everybody for your response.