Re: Define conflict between ext3 and raid patches against 2.2.19

[Hans Reiser <reiser@namesys.com>]

More precisely, as long as you understand that resync requires doing the resync
offline,  and
accept that, and remember it, and your colleagues at work remember it:-), you
can use it.  Personally, I would just go to 2.4 myself.

Hans


Neil Brown wrote:
> 
> On Wednesday September 19, mfedyk@matchmail.com wrote:
> > On Tue, Sep 18, 2001 at 09:08:32PM +1000, Neil Brown wrote:
> > >
> > > You should be aware that ext3 (and other journalling filesystems) do
> > > not work reliably over RAID1 or RAID5 in 2.2.  Inparticular, you can
> > > get problems when the array is rebuilding/resyncing.
> > >
> > > But if you only plan to use ext3 with raid0 or linear, you should be
> > > fine.
> > >
> >
> > Can you point me to an archive that describes how to trigger this bug?
> >
> > Was it in linux-raid or ext3-users or ...?
> >
> > Mike
> 
> I don't remember exactly where or when I read it - either linux-raid
> or linux-kernel.  It was asserted by Stephen Tweedie.
> 
> The problem is that ext3 is very careful about when it writes buffer
> to disk : it won't release a buffer until the relevant journal entry
> is committed.
> 
> However when a RAID rebuild happens, every block on the array is read
> into the buffer cache (if it isn't already there) and then written
> back out again.  This defeats the control that ext3 tries to maintain
> on the buffer cache.
> 
> I don't know exactly what large-scale effects this might have.  It
> could be simply that a crash at the wrong time could leave the
> filesystem corrupted.  But I heard of one person who claimed to get
> filesystem corruption after using reiserfs over RAID1 in 2.2, so maybe
> it's worse than that.
> 
> If you really need to know, I suggest you ask on ext3-users.
> 
> NeilBrown
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