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Date:      Wed, 03 Jul 2013 21:15:50 +1200
From:      Berend de Boer <berend@pobox.com>
To:        Markus Gebert <markus.gebert@hostpoint.ch>
Cc:        freebsd-fs <freebsd-fs@freebsd.org>
Subject:   Re: EBS snapshot backups from a FreeBSD zfs file system: zpool freeze?
Message-ID:  <87zju43sxl.wl%berend@pobox.com>
In-Reply-To: <14A2336A-969C-4A13-9EFA-C0C42A12039F@hostpoint.ch>
References:  <87li5o5tz2.wl%berend@pobox.com> <CA%2BtpaK1jQuKneQsxkVfxJGzXdPdLZfqBM1QWQ0e19nK5t71t1Q@mail.gmail.com> <87ehbg5raq.wl%berend@pobox.com> <20130703055047.GA54853@icarus.home.lan> <6488DECC-2455-4E92-B432-C39490D18484@dragondata.com> <CADBaqmihCB5JP01hLwXTWHoZiJJ5-jkT-Ro=oDwOcKZT_zvEKA@mail.gmail.com> <A5A66641-5EF9-454E-A767-009480EE404E@dragondata.com> <14A2336A-969C-4A13-9EFA-C0C42A12039F@hostpoint.ch>

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>>>>> "Markus" == Markus Gebert <markus.gebert@hostpoint.ch> writes:

    Markus> 1. snapshot the zfs at the same point in time you'd issue
    Markus> that ioctl on Linux
    Markus> 2. take the EBS snapshot at any time
    Markus> 3. clone the EBS snapshot to the new/other VM
    Markus> 4. zfs import the pool there
    Markus> 5. zfs rollback the filesystem to
    Markus> the snapshot taken in step 1 (or clone it and use that)

That seems like a very good first step!

It's unfortunately not automatic, but for recovery purposes it should
do.

Do you think (yes, I will definitely test this), that ZFS can mount a
file system consisting of a couple of disk (raidz2 setup), and access
it even though every disk might be a backup taken at a slighty
different time?

Obviously I'm going to throw away the mounted state and rollback to my
snapshot, but it has to be able to mount a set of disks which might be
in a terrible state first.


    Markus> Also, taking the zfs snapshot should take much less time,
    Markus> because you don't have to wait for the EBS snapshot to
    Markus> complete before you can resume IO on the filesystem. So
    Markus> you don't even depend on EBS snapshots being quick when
    Markus> using the zfs approach, a big advantage in my opinion.

You don't have to wait for an EBS snapshot to complete. That can take
hours. EBS simply takes the moment in time you give the command, and
starts the backup from there. Normal I/O to the disk continues (so
uses some kind of COW system I suppose)

--
All the best,

Berend de Boer


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