On Tue, Apr 17, 2012 at 8:07 AM, Shaohua Li [off-list ref] wrote:

Hi Dan,

On 4/17/12 10:46 PM, Dan Williams wrote:

quoted

On Tue, Apr 17, 2012 at 1:35 AM, Shaohua Li[off-list ref]  wrote:

quoted

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
discard.

It would be great the limitation can be avoided and the code can be
simplified. I didn't follow linux-raid maillist, can you point me the url
of the new bad blocks facility please?

It came in at 3.1 starting with:

commit 2230dfe4ccc3add340dc6d437965b2de1d269fde
Author: NeilBrown [off-list ref]
Date:   Thu Jul 28 11:31:46 2011 +1000

    md: beginnings of bad block management.

    This the first step in allowing md to track bad-blocks per-device so
    that we can fail individual blocks rather than the whole device.

    This patch just adds a data structure for recording bad blocks, with
    routines to add, remove, search the list.

    Signed-off-by: NeilBrown [off-list ref]
    Reviewed-by: Namhyung Kim [off-list ref]

Here is a link to the patch set:
http://marc.info/?l=linux-raid&m=131121721902900&w=2

--
Dan
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