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Date:      Sat, 6 Apr 2013 08:12:49 +1100
From:      Peter Jeremy <peter@rulingia.com>
To:        Joar Jegleim <joar.jegleim@gmail.com>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: Regarding regular zfs
Message-ID:  <20130405211249.GB31958@server.rulingia.com>
In-Reply-To: <CAFfb-hpt4iKSb0S2fgQ16Hp51KLWJew1Se32yX1cUPYi6pp72g@mail.gmail.com>
References:  <CAFfb-hpt4iKSb0S2fgQ16Hp51KLWJew1Se32yX1cUPYi6pp72g@mail.gmail.com>

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On 2013-Apr-05 12:17:27 +0200, Joar Jegleim <joar.jegleim@gmail.com> wrote:
>I've got this script that initially zfs send's a whole zfs volume, and
>for every send after that only sends the diff . So after the initial zfs
>send, the diff's usually take less than a minute to send over.

Are you deleting old snapshots after the newer snapshots have been sent?

>I've had increasing problems on the 'slave', it seem to grind to a
>halt for anything between 5-20 seconds after every zfs receive . Everything
>on the server halts / hangs completely.

Can you clarify which machine you mean by server in the last line above.
I presume you mean the slave machine running "zfs recv".

If you monitor the "server" with "vmstat -v 1", "gstat -a" and "zfs-mon -a"
(the latter is part of ports/sysutils/zfs-stats) during the "freeze",
what do you see?  Are the disks saturated or idle?  Are the "cache" or
"free" values close to zero?

># 16GB arc_max ( server got 30GB of ram, but had a couple 'freeze'
>situations, suspect zfs.arc ate too much memory)

There was a bug in interface between ZFS ARC and FreeBSD VM that resulted
in ARC starvation.  This was fixed between 8.2 and 8.3/9.0.

>I suspect it may have something to do with the zfs volume being sent
>is mount'ed on the slave, and I'm also doing the backups from the
>slave, which means a lot of the time the backup server is rsyncing the
>zfs volume being updated.

Do you have atime enabled or disabled?  What happens when you don't run
rsync at the same time?

Are you able to break into DDB?

>In my setup have I taken the use case for zfs send / receive too far
>(?) as in, it's not meant for this kind of syncing and this often, so
>there's actually nothing 'wrong'.

Apart from the rsync whilst receiving, everything sounds OK.  It's
possible that the rsync whilst receiving is triggering a bug.

--=20
Peter Jeremy

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