Re: Does raid5 have error handling while reading?

["NeilBrown" <neilb@suse.de>]

On Fri, May 22, 2009 6:10 pm, Xu Yuehai wrote:
> I know that if the read request of raid5 is handled by
> chunk_aligned_read, there is no error handling in raid5. But, if this
> read request is not aligned, that's say, raid5 need stripe_head to
> deal with this request. I find in the code of 2.6.27 that there is no
> error handling if this read request fail, I remember in older kernel,
> some operations should be done such as compute_block. Am I right?

If chunk_aligned_read results in an error, then the request
is re-tried through the stripe cache.  I would call that "error handling".

If the cache finds that a drives is failed, the data is calculated
from the other drives, though the code is not a straight forward
as it used to be.
See fetch_block5 which sets STRIPE_OP_COMPUTE_BLK which causes
ops_run_compute5 to do the work (or to schedule the work on separate
hardware).

NeilBrown