Messages in this thread |  | | From | Neil Brown <> | Date | Thu, 20 Sep 2001 08:35:04 +1000 (EST) | Subject | Re: Define conflict between ext3 and raid patches against 2.2.19 |
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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.
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