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Date:      Tue, 13 Dec 2016 15:44:58 -0800
From:      Aleksandr Miroslav <alexmiroslav@gmail.com>
To:        freebsd-questions@freebsd.org
Subject:   zfs (zxfer) replication -- "holes" in backups?
Message-ID:  <CACcSE1xb1k330wJ6tyvQ2Vfv8bFKT97cbDx=OQaES8V8pOQ9DA@mail.gmail.com>

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I'm using zxfer to replicate my ZFS snapshot to another host. Occasionally,
for whatever reason, zxfer can't replicate a particular snapshot.

What I find is that later when zxfer tries again, it skips that snapshot it
couldn't replicate and sends a newer one. This leaves the back up server
with with a "hole", i.
e. a missing snapshot.

For example: I have server with the following snapshots:








*zroot/usr/home@zfs-auto-snap_daily-2016-11-19-00h00  [EXISTS ON
BACKUP]zroot/usr/home@zfs-auto-snap_weekly-2016-11-20-00h00 [EXISTS ON
BACKUP]zroot/usr/home@zfs-auto-snap_daily-2016-11-21-00h00  [EXISTS ON
BACKUP]zroot/usr/home@zfs-auto-snap_daily-2016-11-22-00h00  [EXISTS ON
BACKUP]zroot/usr/home@zfs-auto-snap_daily-2016-11-23-00h00  [MISSING
BACKUP][...]zroot/usr/home@zfs-auto-snap_hourly-2016-12-13-14h00 [MISSING
BACKUP]zroot/usr/home@zfs-auto-snap_hourly-2016-12-13-15h00 [EXISTS ON
BACKUP]*

Here is my backup server:

*zroot/usr/home@zfs-auto-snap_daily-2016-11-19-00h00*
*zroot/usr/home@zfs-auto-snap_weekly-2016-11-20-00h00*
*zroot/usr/home@zfs-auto-snap_daily-2016-11-21-00h00*
*zroot/usr/home@zfs-auto-snap_daily-2016-11-22-00h00*
*zroot/usr/home@zfs-auto-snap_hourly-2016-12-13-15h00*

Notice that I have backups until the 22nd of November, and there is a huge
gap until the 13th of December.


Usually these gaps are small, one or two missing snapshots...in this
particular case, the backup server was offline for a bit.

When zxfer starts up again, I thought it would resume sending from the last
one, it apparently doesn't do that.

The way I have fixed this manually in the past is to delete the newest
backup on the target server and run zxfer manually. Recently, the missing
backups have gotten so large that this is somewhat painful to do.

Is there something in zfs/zxfer I can change such that the backup server
will always have the latest copy as the master?

thanks,
Alex



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