Incremental backup using zfs send

[glowkrantz]

Hi martineau,

Originally Posted by martineau

Thanks for the patch, I started to look at it and I have 1 questions?

Why zfs_purge_snapshot is called before the backup is tried?
I think it should be called only if the backup succeed and just before zfs_rename_snapshot.

If amanda try a level 0 and it failed, it can try a higher level on the next run.

I think it was because I managed to get in a failure mode where I had a snapshot that had not resulted in a valid backup and the next time I tested, amanda choose the next higher level, as in I have valid 0, 1 and 3 but no valid 2 backup. So by doing it this way, I made sure the next highest backup level was the failed one, in the example above, a level 2 backup.

Hope this makes sense ;-)

There is still a failure mode when there will be an lost current snapshot that is not removed if the client crashes before amanda finishes and we may need to remove that in the zfs_purge_snapshot as we otherwise will have one failed backup before the client is in sync again.

/glz

[glowkrantz]

Hi Nick,

Originally Posted by nick.smith@techop.ch

Hi all,

I think the current proposal will have significant performance issues with the piping the output through wc (espcially during the estimate phase!).

Could you not use :

$cmd = "$self->{pfexec_cmd} $self->{zfs_path} get -Hp -o value used $self->{filesystem}\@$self->{snapshot}"

for snapshots with level > 0?

Regards,

Nick

I understand and am searching all over the place for other ways t do it.

This method is anyhow faster than with snapshot/gtar, especially on compressed filesystems. We have a few of them, handling Oracle and PostgreSQL backups and logs and with 2.2 times compression ratio on 30 to 40G referenced, it's almost a factor of 3.

I have no actual numbers for my test system just now but I was able to go back to the default etime when I switched from snapshot/gtar to this setup.

/glz

[nick.smith@techop.ch]

Originally Posted by martineau

You didn't try to remove files.

If you remove /rpool/test/sol-nv-b101-x86-dvd.iso.1 before creating level 3 snaphost, then the reference for level 3 snapshot will be 7.37G, you wil get:
# zfs list -r rpool/test
NAME USED AVAIL REFER MOUNTPOINT
rpool/test 10.4G 305G 10.4G /rpool/test
rpool/test@0 17K - 2.15G -
rpool/test@1 17K - 5.22G -
rpool/test@2 17K - 7.37G -
rpool/test@3 0 - 7.37G -

but the backup will be 2.15G, how do you compute it?

Ah well yes, very good point!

I'll play around a bit more and see if examining both the used and refer values for all the snapshots we can get a solution.

Not directly related but of interest: I asked the zfs-discuss mailing list about what output 'zfs send -v snapshot-name' should produce and got the following :

Originally Posted by chris.kirby@sun.com

Nick,

Specifying -v to zfs send doesn't result in much extra information, and only in certain cases. For example, if you do an incremental send, you'll get this piece of extra output:

# zfs send -v -I tank@snap1 tank@snap2 >/tmp/x
sending from @snap1 to tank@snap2
#

zfs recv -v is a bit more chatty, but again, only in certain cases.

Output from zfs send -v goes to stderr; output from zfs recv -v goes to stdout.

-Chris

Regards,

Nick

[martineau]

Originally Posted by glowkrantz

Hi martineau,

I think it was because I managed to get in a failure mode where I had a snapshot that had not resulted in a valid backup and the next time I tested, amanda choose the next higher level, as in I have valid 0, 1 and 3 but no valid 2 backup. So by doing it this way, I made sure the next highest backup level was the failed one, in the example above, a level 2 backup.

Hope this makes sense ;-)

There is still a failure mode when there will be an lost current snapshot that is not removed if the client crashes before amanda finishes and we may need to remove that in the zfs_purge_snapshot as we otherwise will have one failed backup before the client is in sync again.

/glz

amanda should not increase the level if the backup was invalid.
Do you remember what was invalid?
Did it was a dump to holding disk or direct to tape?
Do the backup was successful but the server was not able to save it to holding disk or tape?
Or it was a zfs error and zfs didn't sent the error to the server?
Or something else?

[glowkrantz]

I think you are correct, this is not a problem. My failed sequence was probably due to a bug in the original script I had and after getting that right, I never removed the purge phase. The way it's done now will force Amanda to go one level lower than needed after a failed backup. The purge was originally there to remove any stray current snapshots but got changed while I was testing the scripts to do the delete of the expected snapshot.

I have created a new version working the expected way, I will submit it as soon as it has a few backups under it's belt.

/glz

[martineau]

I committed your previous patch with many fix.
If you want to send me a new patch, send it relative to the current source tree.

[glowkrantz]

While testing 20090122, I have found one more thing and that's the level 0 estimate on a compressed file system. We need to multiply with the compression ration to get closer to the actual backup size.

Attached patch adds this to the estimate call.

Otherwise, this seems to be working just fine.

/glz