fsck of big disk

[Josh Paetzel]

On Tuesday 11 December 2007 09:19:46 am Valerio Daelli wrote:
> Hi,
> thanks a lot for your answer.
>
> > > we have a freshly installed FreeBSD 6.2 machine with a gstriped
> > > external disk, of 5.3Tb. The disk is composed of two slices of 2.6 Tb.
> > > We are trying to have a (background) fsck of it but few hours later
> > > since the start of the check
> > > the host get unresponsive: it responds to ping but it doesn't let
> > > login anyone, nor by ssh
> > > nor by console.
> >
> > What do you get if you press Control-T on the console when it is
> > unresponsive?
>
> We are not able to login via console nor via ssh.
> Pheraps you suggest me to press Control-T on the console even if I am not
> logged on. I did not try, sorry.
>
> > When you do a background fsck there is a point at which a snapshot of
> > the filesystem is taken, although I'd say that happens at the beginning
> > of the check. The problem is that with 5.3 Tb, it may take quite a while
> > to take the snapshot, and during that time the system blocks any process
> > that tries to write to the filesystem. Maybe that's what you are
> > experiencing.
>
> What you explained us sounds very interesting. But anyway we simply
> solved by disabling background fsck on such a big partition. We had
> panics and reboot
> and we did not want to risk on a production host.
> Bye
>
> Valerio Daelli

What you are probably running in to is memory starvation.  In my experience 
fsck on a moderately filled disk uses something on the order of 1 gig of RAM 
per TB of filesystem.  If you have this in an array with less than 4 gigs of 
RAM it's possible that it was just buried in swap and spending all it's time 
moving pages in and out as opposed to doing anything useful.


-- 
Thanks,

Josh Paetzel

PGP: 8A48 EF36 5E9F 4EDA 5A8C 11B4 26F9 01F1 27AF AECB
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