On 4/18/12 4:26 AM, NeilBrown wrote:
On Tue, 17 Apr 2012 07:46:03 -0700 Dan Williams<dan.j.williams@xxxxxxxxx>
On Tue, Apr 17, 2012 at 1:35 AM, Shaohua Li<shli@xxxxxxxxxx> wrote:
Discard for raid4/5/6 has limitation. If discard request size is small, we do
discard for one disk, but we need calculate parity and write parity disk. To
correctly calculate parity, zero_after_discard must be guaranteed.
I'm wondering if we could use the new bad blocks facility to mark
discarded ranges so we don't necessarily need determinate data after
...but I have not looked into it beyond that.
The bad blocks framework can only store a limited number of bad ranges - 512
in the current implementation.
That would not be an acceptable restriction for discarded ranges.
You would need a bitmap of some sort if you wanted to record discarded
This appears to remove the unnecessary resync for discarded range after
or discard error, eg an enhancement. From my understanding, it can't
limitation I mentioned in the patch. For raid5, we still need discard a
stripe (discarding one disk but writing parity disk isn't good).
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