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SubjectRe: [patch 4/5] fail-injection capability for disk IO
On Wed, 23 Aug 2006 14:03:55 +0200
Jens Axboe <axboe@suse.de> wrote:

> On Wed, Aug 23 2006, Akinobu Mita wrote:
> > This patch provides fail-injection capability for disk IO.
> >
> > Boot option:
> >
> > fail_make_request=<probability>,<interval>,<times>,<space>
> >
> > <probability>
> >
> > specifies how often it should fail in percent.
> >
> > <interval>
> >
> > specifies the interval of failures.
> >
> > <times>
> >
> > specifies how many times failures may happen at most.
> >
> > <space>
> >
> > specifies the size of free space where disk IO can be issued
> > safely in bytes.
> >
> > Example:
> >
> > fail_make_request=100,10,-1,0
> >
> > generic_make_request() fails once per 10 times.
>
> Hmm dunno, seems a pretty useless feature to me.

We need it. What is the FS/VFS/VM behaviour in the presence of IO
errors? Nobody knows, because we rarely test it. Those few times where
people _do_ test it (the hard way), bad things tend to happen. reiserfs
(for example) likes to go wobble, wobble, wobble, BUG.

> Wouldn't it make a lot
> more sense to do this per-queue instead of a global entity?

Yes, I think so. /sys/block/sda/sda2/make-it-fail.

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