Doing the deed ! Unsplitting mirrors

[Simon R Wootton]

My previous post asked about unsplitting mirrored disks - thanks for the replies - very useful. My next question refers to doing it on a live system running 600 users. Is it safe to do ? Do I risk losing any data ? What's the worst that could happen ? Thanks in advance for the continued help & support.

P.S. This thread has been moved from  Disk to HP-UX > sysadmin. -HP Forum Moderator

[Martin Johnson · Accepted solution]

Nothing bad should happen to your system. However, the data on the unmirrored disks will probably be inconsistant or corrupted due to the open files at the time of the split. Corruption is more likely in databases than flat files.

To insure a complete uncorrupted copy of the data is on the unmirrored disks, all files must be closed prior to splitting the mirror.

HTH
Marty

[S.K. Chan]

If I can recall, from your previous post (assuming you do not have OnlineJFS) you'll have to umount the FS anyway to increase it and then mount it back. That means you'll have to kick the users out from the FS before you can umount it. Lvreducing a mirror copy is not a problem (on a running system) but lvreducing the size of a logical volume is. So in your case you'll be fine. The worst that could happened is during the "lvreduce -m 0" it hung on you and that could happen if LVM is not fully patched and "possible" IO error. So far I have not had lvreducing of a mirror copy failed on me yet. Having said all that, if you want to be extra-cautious, make sure ..
1) Back it up
2) Do not do this on a live system

[Bill McNAMARA_1]

You bought mirrordisk so you can do this. The problem will be resyncronising the mirrors back after the split. You must be extremely careful with the lvmerge syntax.
Data will not be lost, however, you will be at a single point of failure at the time, to avoid this you could create a third mirror then split the second.. but not recommended with 600 users due to heavy disk ios.

Worst that could happen is command syntax error, primary mirror failing when split, merging the split into the primary on resynchronisation rather than vice versa.

Online filesystem resizing can only be done with fsadm (online JFS)

Later,
Bill