Using fssnap on Solaris 9 for backup
I have been using fssnap to backup the whole server for 2 years. Recently, I got some problem with it.
My servers are using Solaris 9, which using fssnap to create a partition image on a separate partition. Then, the image will be picked up by tape drive.
Recently, we got problems with these servers. Servers hung intermittently, no definite time period. When it hung, root can only login (through console or telnet), but without a prompt. All I can do is to go to sc prompt to issue "break" command, back to console and do "sync".
I had sent the core dump file to SUN support, they replied that the problem is related to fssnap, and asked me to patch the machine.
I have a question in my mind because we re-establish the fssnap image after images have been backed up to tape drive, and leave the re-established image on the other partition all day, until next backup time. The purpose of this is to maintain a most recent image of the box at all time fro recovery. Is it necessary to do that?
Thanks in advance.
[1050 byte] By [
DougTecha] at [2007-11-26 14:08:17]
# 1
> I have a question in my mind because we re-establish
> the fssnap image after images have been backed up to
> tape drive, and leave the re-established image on the
> other partition all day, until next backup time.
I'm not sure what you mean by "re-establish" here. This isn't a mirror where you redo the sync after you're done. With fssnap, you just throw away the old data. There's nothing to re-establish.
Or are you saying you create a new fssnap image after the tape backup completes? Do you ever send it to tape?
> The
> purpose of this is to maintain a most recent image of
> the box at all time fro recovery. Is it necessary to
> do that?
How would you access the fssnap image on the box for a recovery? If the box crashes, the fssnap image is gone, right? I guess it depends on what you mean by "recovery". You could pull individual files from it quickly.
--
Darren
# 2
I think you might have misunderstood what fssnap does.
It creates a virtual snapshot of a filesystem, at an instant in time, so that you have an unchanging object to backup.
Otherwise if files are being changed while you backup, you can get inconsistent results.
It doesnt actally store the whole filesystem in some reusable way. In itself its no use for restoration per se. Its simply a tool to allow other backup techniques to work more consistently.
How it works is it enables produces a virtual copy of the filesystem using copy on write.
So the backing store starts empty. When ever a block on the original filesystem is changed, it copies the original block to the backing store, before making the change.
So, when you access the virtual snapshot, it first checks the backing store, if the blocks not there it knows the block on the original hasnt been changed and returns that.
So the backing store is intimately associated with a filesystem. It only contains a more or less random scattering of blocks from the filesystem. By itself its no good to you.
And if the machine reboots or something. Then the backing store and the filesystem are no longer perfectly matched so can't be used.
So the usual way to use a snapshot is, immediately prior to starting backup to tape, you snapshot. Then backup the snapshot to tape and delete it.
Deleting a snapshot doesnt require any effort. The the original filesystem is always the "true" copy. It doesnt have to merge the snapshot in or anything. It just stops recording the actions.
Theres little point leaving a snapshot on all the time. It will just sit there growing as files are changed. It would allow you to see files as they were a day ago. But unless you need to do that frequently, the last backup tape will do that.
It you were trying to use fssnap to do "backup to disk", then fssnap by itself isnt enough.
what you need to do is somethink like rsync the filesystem to another partition.
How fssnap helps is, if your data is sensitive to consistency issues then you can snapshot and rsync the snapshot.
