Disk Mirroring

[Jeff Sadowski_2]

I have a question on mirroring.
We setup disk mirroring on one of the computers and shipped it to the location it is now. One of the disks failed to come up when it reached its destination. This was some time ago. Now that disk became active. I've been told it mirrored itself back onto the disk they have been using all this time.
So my boss is asking me to find out why and how to make it so that mirroring is done with the more current data. Not having direct access to the disks I'm not sure if it did mirror it off the older disk image or if the newer image still exists but the older one is masking it. Any help or information to this would be helpful thanks.

P.S. This thread has been moved from HP-UX Technical Documentation to LVM and VxVM. -HP Forum Moderator

[Jeff Sadowski_2]

More info this is a rx2600 with
HP-UX 11iv23

[A. Clay Stephenson]

What OS?

[Jeff_Traigle]

MirrorDisk/UX brought the disk that was inactive up to date with the disk that was active. (It would take some manual work to get the system to use the "old image" from the inactive disk to overwrite the disk you've been using.) That's the way it works... if a disk fails and you replace it or it starts behaving itself again miraculously, the latest information from the one that kept running is copied to the new/reactivated one to be sure all current data is available.

You can check if the disks are synced or not by the follwoing command:

lvdisplay -v | more

You should see all extents synced and available. If any are stale, you try to run "vgsync" to see if that works, but most of the time stale extents mean a failing or failed disk.

[Jeff Sadowski_2]

Thats what is suppose to happen but what occurred is what I described the outdated disk mirrored to the up to date disk. Luckily this customer backs up regularly and got his data off of backup but now I need to find out how to prevent this in the future.

Very well could be that the disks are out of sync though I'll have my customer run
"lvdisplay -v /dev/vg01/lv01" or what ever the logical volumes name is. What would I be looking for? What kind of output can I expect if they are out of sync? What if there in sync?

[Alzhy]

If disk1 was your primay and disk2 is your alternate -- and over this time disk2 was active with disk1 inactive( for whatever reason) - and disk1 became active the question to ask is ?

Did disk1 become active whilst disk2 is active (booted with the OS)? If that's the case - which appear is not, then disk1 should now contain disk2's data.

IF disk1 became "active" from Cold Start -- then I would say your disk2's current data is probably history as disk1 would have pushed/synched its changes to disk2.

I could be wrong though as I've ever actually experimented with this on LVM managed systems.

[Radhakrishnan Venkatara]

One of the possiblity is the inactive disk might have got activated in the cold reboot. So the old data might have got remirrored.
If you could see the current status of the mirror you could probably identify it.

Regards

Radhakrishnan