Date: Sun, 30 May 2010 22:35:59 -0400 From: David Magda <dmagda@ee.ryerson.ca> To: Kirk Strauser <kirk@strauser.com> Cc: FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org> Subject: Re: Make ZFS auto-destroy snapshots when the out of space? Message-ID: <19664824-1B23-4E5F-BC12-BB4D59A9C8AA@ee.ryerson.ca> In-Reply-To: <F5E2E18E-A870-4600-9D4C-D0BE9BF68CF1@strauser.com> References: <4C017419.9010909@strauser.com> <4632C12D-2B1E-4073-B2C9-E9D15C212EF1@ee.ryerson.ca> <F5E2E18E-A870-4600-9D4C-D0BE9BF68CF1@strauser.com>
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On May 30, 2010, at 22:17, Kirk Strauser wrote: > For instance, what happens if a disk-full condition occurs 2 minutes > before the cron job would have run that would've averted it? At what > level do you trigger deletions that would both 1) provide enough of > a safety margin that disk-fulls are unlikely, but 2) allow the > snapshots to take advantage of as much storage as possible? What happens now when your UFS file system gets full? :) The situation is no worse than that in the case of a pool filling up, regardless of whether it's because of an abundance of snapshots or simply lots of "regular" user data. > But we have all sorts of daemons that do stuff behind our back. Yes, but they're daemons, not kernel code. As a general rule I like to be able to do a ps(1) on any one of my systems and be able to describe what every single PID does. If it's Amanda, I know what its purpose is; if it would be something called auto-snap(8) or auto-scrub(8) or auto-snap-clean(8) then I'd have to learn what those are. An event framework would certainly be helpful in a general sense (Linux has event(3) AFAIK), and that could certainly be useful for purging snapshots during resource constrained situations. But even if we don't have it, I doubt a fork(2) from cron(8) and a statfs(2) would be onerous on a system. :) > That just scrubs the pools, ie verifies checksums and data > consistency. Yes, I know, it was the general principle I was going after: if you want something periodic to be checked, you should run it from cron/SMF/ launchd/etc.
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