Date: Sun, 20 May 2007 13:28:41 -0700 (PDT) From: Gore Jarold <gore_jarold@yahoo.com> To: Scott Long <scottl@samsco.org> Cc: freebsd-fs@freebsd.org Subject: Re: dangers of delaying an fsck on busy fileserver ? Message-ID: <653845.99663.qm@web63012.mail.re1.yahoo.com> In-Reply-To: <464F3178.1020909@samsco.org>
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--- Scott Long <scottl@samsco.org> wrote:
> Gore Jarold wrote:
> > --- Scott Long <scottl@samsco.org> wrote:
> >
> >
> >> In an ideal world, the only consequence of
> delaying
> >> bgfsck is that
> >> not all filesystem blocks will be marked free
> that
> >> should be. So
> >> if you deleted a large tree of files before the
> >> crash, those blocks
> >> might still show up in use until bgfsck
> completes.
> >
> >
> > Thank you. Would _you_ do this with valuable data
> ?
> >
>
> Very good question =-) If you're using softupdates
> then any
> damage will have been done when the hard shutdown
> happens; bgfsck
> won't create any new damage. The biggest problem of
> bgfsck beyond
> the i/o slowness and near deadlocks that it can
> create (modulo the
> fixes that the Kostik is working on) is that if it
> does encounter
> damage that it can't fix automatically, it exits and
> leaves the
> filesystem inconsistent. So you need to keep a very
> close eye on
> your logs and check for this, then schedule downtime
> when it happens
> so you can babysit a full fsck.
Ahhh... I think you may have misunderstood my original
question. What I am saying is, I don't _ever_ want to
do a background fsck. My systems are too busy (and
have too large of disks) to deal with the (current)
baggage of making a 4 TB snapshot and then
bg_fsck'ing.
What I am saying is the following:
- I set background_fsck_delay="86400"
- I tell datacenter techs NOT to call me when the
system crashes - just to hit reset.
- users bang on the system, as normal, for X hours -
all the while the filesystems are _dirty_ and nothing
is being done about it
- I wake up hours later, unmount the filesystems, and
foreground fsck them
My goal in all of this is to keep from being woken up
in the middle of the night. I don't care about the
downtime to the system when I eventually do foreground
fsck them, I just don't want to do it in the middle of
the night _and_ I don't want my users to have to sit
around waiting for me to do the fsck _on top of_ the
fsck downtime itself.
So ... comments ? I _suspect_ the conclusions are
about the same - running on a dirty FS is the same as
running on a dirty FS while being bg_fsck'd ... but I
want to make sure...
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