ADSM-L

More on fssnap on Solaris

2005-08-08 22:35:01
Subject: More on fssnap on Solaris
From: Stuart Lamble <adsm AT CAROUSEL.ITS.MONASH.EDU DOT AU>
To: ADSM-L AT VM.MARIST DOT EDU
Date: Tue, 9 Aug 2005 12:34:06 +1000
I've done some experimentation. So far, I've found that TSM will not
backup a filesystem image for a fs mounted from /dev/fssnap/N, but it
will backup the image as a raw image. This then raises the question
of consistency -- making sure that a given filesystem is backed up
with the same name every time.

As an example, suppose I have three filesystems (A, B, and C) that I
want to backup as an image using fssnap. If I create a snapshot for
A, it will be given the snapshot device /dev/fssnap/0. If I then back
it up and delete the snapshot, and then create another snapshot for
filesystem B, filesystem B will also get the fssnap device /dev/
fssnap/0.

Conversely, if I create a snapshot for filesystems A and B
concurrently, they will be given different numbers. (0 and 1).
Subsequent creations of snapshots will give them the same numbers as
they were given in the first instance (so if filesystem A has no
snapshot, and I ask for B to have a snapshot created, it will be
given /dev/fssnap/1 -- not 0.) I have not experimented beyond two
simultaneous filesystems as yet.

Based upon my experimentation and reading of the manuals, I get the
feeling that there is no way to tell TSM, "Back up this device, but
name it as /foo/bar rather than /baz/bam". Can anybody shed any light
that may be of use in backing up filesystems in this manner, whilst
keeping it clear enough that we can easily determine which device is
associated with a given filesystem, and that this mapping is kept
consistent? Am I wrong? If not, I fear that this technique will be
rendered useless to us.

There are other options that I can pursue, as I've indicated before,
and I'm about to start on them; I was hoping that the collected TSM
gurus might be able to point me in another direction that I haven't
yet noticed.

The other option, of course, is to ask IBM to support fssnap in a
future release, but since that's not likely to happen before 5.4 (at
a guess) ...

Thanks for all advice that you can give,

Stuart.

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