Date: Thu, 04 Jul 2013 12:55:36 +1200 From: Berend de Boer <berend@pobox.com> To: "Steven Hartland" <killing@multiplay.co.uk> Cc: freebsd-fs@FreeBSD.org Subject: Re: EBS snapshot backups from a FreeBSD zfs file system: zpool freeze? Message-ID: <87bo6j3zzr.wl%berend@pobox.com> In-Reply-To: <BD8B4240539A46FC9FB86615A7F675CA@multiplay.co.uk> References: <87li5o5tz2.wl%berend@pobox.com> <BD8B4240539A46FC9FB86615A7F675CA@multiplay.co.uk>
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>>>>> "Steven" == Steven Hartland <killing@multiplay.co.uk> writes:
Steven> Not been following the thread really so excuse if this has
Steven> already been mentioned ;-)
Not yet.
Steven> There is a zpool freeze <pool> which stops spa_sync() from
Steven> doing anything, so that the only way to record changes is
Steven> on the ZIL.
Pardon my ignorance, I don't really understand this. First of all, is
there a way to recover from a freeze? I.e. do I need to unfreeze?
What you're saying is that it is a one way street only? I just did
this on my semi-production server to see what is going to
happen. Nothing so far.
I had a look at the code, this is what it calls:
static int
zfs_ioc_pool_freeze(zfs_cmd_t *zc)
{
spa_t *spa;
int error;
error = spa_open(zc->zc_name, &spa, FTAG);
if (error == 0) {
spa_freeze(spa);
spa_close(spa, FTAG);
}
return (error);
}
And spa_freeze is this:
void
spa_freeze(spa_t *spa)
{
uint64_t freeze_txg = 0;
spa_config_enter(spa, SCL_ALL, FTAG, RW_WRITER);
if (spa->spa_freeze_txg == UINT64_MAX) {
freeze_txg = spa_last_synced_txg(spa) + TXG_SIZE;
spa->spa_freeze_txg = freeze_txg;
}
spa_config_exit(spa, SCL_ALL, FTAG);
if (freeze_txg != 0)
txg_wait_synced(spa_get_dsl(spa), freeze_txg);
}
All nicely undocumented code.
Steven> The comment in the zpool_main is: "'freeze' is a vile
Steven> debugging abomination" so it's evil but might be what you
Steven> want if you're up to writing some code.
Yeah!
But thanks for digging this up, I hadn't expected undocumented
commands for zpool!
Steven> For more info have a look at ztest.
Another undocumented tool. How would I use this in this case?
--
All the best,
Berend de Boer
------------------------------------------------------
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