Re: RAID6 rebuild stuck

On Tue, 02 Oct 2012 21:35:05 +0100 John Robinson
[off-list ref] wrote:

On 02/10/2012 21:29, NeilBrown wrote:

quoted

On Tue, 02 Oct 2012 20:51:31 +0100 John Robinson
[off-list ref] wrote:

quoted

On 02/10/2012 16:56, Brian Candler wrote:

quoted

On Tue, Oct 02, 2012 at 03:56:42PM +1000, NeilBrown wrote:

quoted

Lesson: always do a read test as well as a write test!

And there was me thinking that drives read back data after writing it -
clearly they do not :-)

Would it be worth adding a re-read onto the end of the usual read
failure reconstruct-write cycle?

What?  Read twice?

We already read after the write when attempting to fix a failure.

I didn't realise you already did that.

quoted

I suspect it doesn't do much good though as the data is in cache in the drive.

No, maybe not. There isn't an option you can add to ask for an uncached 
read? But I dare say you'd have thought of that already if there was :-)

Maybe setting REQ_FUA would work.  Or maybe it would cause crashes and random
data corruption.  I suspect most people think of REQ_FUA as being associated
with WRITEs.  Maybe I'm to cynical, but this would be extremely hard to test,
and I don't feel up to the code review that would be required to provide
sufficient confidence :-(

NeilBrown

Cheers,

John.

--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html