Date: Thu, 04 Jul 2013 07:39:26 +1200 From: Berend de Boer <berend@pobox.com> To: "Mark Felder" <feld@feld.me> Cc: freebsd-fs <freebsd-fs@freebsd.org> Subject: Re: EBS snapshot backups from a FreeBSD zfs file system: zpool freeze? Message-ID: <87mwq34emp.wl%berend@pobox.com> In-Reply-To: <op.wznad7th34t2sn@tech304.office.supranet.net> 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> <871u7g57rl.wl%berend@pobox.com> <op.wznad7th34t2sn@tech304.office.supranet.net>
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>>>>> "Mark" == Mark Felder <feld@feld.me> writes:
Mark> On the other hand, every time I read about "block storage
Mark> snapshots" -- even if you quiesce the filesystem -- I start
Mark> to get really itchy thinking about the likeliness a high TPS
Mark> database is going to end up with corruption and require
Mark> recovery. :)
That's not how it works: if you freeze the file system at a consistent
point, you can use the roll-forward/backward capabilities of your db
to come back clean.
You can do this even fancier. Mysql or Mongo allow you to flush their
caches as well + put in place a global lock of the database.
Then you freeze the file system, take the snapshot, unfreeze file
system, then unfreeze mysql.
People have been using this for many years, for example a famous
utility for this was mylvmbackup: http://www.lenzg.net/mylvmbackup/
ZFS should work really well here, and people probably use zfs
snapshots in this manner. If performance is an issue, you do this on
the slave obviously.
But I don't get the itchy part: if a disk is just software, I can copy
it. I want to copy it. To another data centre (zone) for
example. That's a trivial operation in EBS, and you can clone huge
disks this way in minutes. Doing an zfs send/recv is just laughably
primitive and slow compared to this. It would take me days to send a
full snapshot this way.
Mark> This really does sound like Amazon needs to provide whatever
Mark> mechanism to communicate between the host and the guest so
Mark> this EBS snapshot can take place.
Again, my request has *nothing* to do with EBS. If you have multiple
disks in your pool, how can you make a backup you can restore from, at
the hardware level.
--
All the best,
Berend de Boer
------------------------------------------------------
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