topic Snapshots snapof= in Operating System - HP-UX

Snapshots snapof=

Ray Humpage — Tue, 28 Feb 2006 13:40:44 GMT

This should be an easy one. I think I know the answer but because it has to do with backups I want a second opinion.

I have the following command which creates a snapshot.

/usr/sbin/mount -F vxfs -o snapof=/dev/vgprd/prd /dev/vgprd/prdbu /buprd

Now that I have the snapshot.....
I backup using the new mount point of /buprd (/dev/vgprd/prdbu) not my original mount point /prd (/dev/vgprd/prd). Correct???

Re: Snapshots snapof=

A. Clay Stephenson — Tue, 28 Feb 2006 13:53:11 GMT

Yes, that is correct although my convention (and therefore, by definition, the "correct" convention) is to use "snap" as the prefix so that /buprd would become /snapprd. You would backup using the "/buprd" mountpoint but the regular application continues to use normal mountpoint.

You haven't quite got the command right; I assume that your filesystem is called /u01/myfilesystem.

mount -F vxfs -o snapof=/u01/myfilesystem /dev/vgprd/prdbu /snapmyfilesystem

You use the mountpoint of the original filesystem rather than the underlying block device. The 2nd argument should be a block device ~ 15% as large as the original filesystem. It is used as the snapshot buffer.

When you all all done, you issue a umount /snapmyfilesystem and you are done. I typically also remove the snapshot mountpoints at this time and recreate them just prior to the next snapshot.

Re: Snapshots snapof=

Ray Humpage — Tue, 28 Feb 2006 14:10:50 GMT

I am so glad that I asked my question!

I have been running it using the block device name instead of the mount point for a couple of months now. Glad I haven't had an outage and had to restore. Thanks.

Re: Snapshots snapof=

A. Clay Stephenson — Tue, 28 Feb 2006 14:31:58 GMT

Actually I should have said that either the mountpoint or the block device could be used as the snapof= argument. It's just that, if the mountpoint is used, the association (at least with respect to us dumb humans) to the snapshot mointpoint is much more obvious.

e.g.

snapof=/prd /dev/vgprd/prdbu /snapprd
is clearer than
snapof=/dev/vgprd/prd /dev/vgprd/prdbu /snapprd

It's even more clear when the standard lvol1, lvol2, ... convention is used.