reverse sync a BC for a specific lvol

[Edgar_8]

We have an XP256 shared between HOSTA and HOST, is it possible to reverse pairresync from HOSTB to HOSTA
specifying which lvol within a vg to be reversed synced? If so can someone please let me know what
needs to be changed (ie.horcm.conf) to do the above.

Your assistance in this regard is most appreciated!

[Steven E. Protter]

I'd kind of have to know what reverse pair sync means.

Please post your configuration.

Its probably possible to use mirror/ux to duplicate lvol data, split mirrors as part of some larger re-arrangement of the data.

SEP

[CAS_2]

Hi

Raid Manager can resync or reverse resync two LUNs, not two lvols in VGs. If your lvols match entires LUNs, then Raid Manager will do.

If your lvols are spread into several LUNs, the reverse resync will concern every lvol in the LUN.

P.D: the right forum to post this issue is Storage/Disk Array.

[Mel Burslan]

I am not my organizations SAN administrator but I remember this was a big caution point in our initial training sessions when we got our XP1024, as it is very easy to do and can be done even by accident (ahem HP/Hitachi has to be a little more careful on this end)
Again as far as I can remember, you do not need to change anything inside horcmX.conf file. You just need to change one of the command line switches to indicate you want a reverse sync, i.e., change the roles of source and target. But I can not remeber what the switch exactly was. And since you will be talking about massive data loss, I would not take any chances and talk to your SAN support person from HP. It is a very simple command to perform with potentially catastrophic consequences. Keep that in mind.

[Edgar_8]

Hi CAS,

So what you saying is that if a vg is setup as RAID 5 then one cant selectively pairresync -restore a specific lvol?

Thanks in advance!

[Simon Hargrave]

Be very careful. Assuming you mean you want to restore a previously split logical volume over your current primary volume?

business copy works with whole physical volumes, not logical volumes. in any volume group your logical volume is likely spread across multiple physical volumes.

also, you MUST NOT restore anything but a WHOLE volume group. Even if one of your logical volumes uses all of exactly one physical volume within the volume group - this will cause the volume group to be out of sync, and likely data loss.

if you have a business requirement to effectively roll-back individual logical volumes from time to time, then you must from that start have each volume (or groups of volumes) on its own volume group.

Only ever restore a volume group at a time, using ALL disks within that group.

[CAS_2]

Hi Edgar.

You cannot restore selectively LVOLs, you should restore entire VGs because physical volumes (PVs) holds VG metadata into their header. This metadata resides into /etc/lvmtab of the system. If you resync or reverse resync JUST one PV, this metadata in headers won't match metadata in /etc/lvmtab ====> LVM conflict

[Geoff Wild]

You can not restore a single lvol - unless that lvol is the only lvol in a vg - it's just like on EMC - as you have to restore a whole disk - not part - as it works at the frame level - bit by bit - not OS....

Rgds...Geoff