[dm-devel] [Lsf-pc] [LSF/MM TOPIC] a few storage topics
Andreas Dilger
adilger at dilger.ca
Wed Jan 25 06:11:33 UTC 2012
On 2012-01-24, at 5:23 PM, NeilBrown wrote:
> On Thu, 19 Jan 2012 01:42:12 +0200 Boaz Harrosh <bharrosh at panasas.com> wrote:
>
>>>> Or possibly modify md-raid5 not to snapshot dirty pages prior to xor/write?
>>>> (I never really bothered to find out if it really does this.)
>>
>> md-raid5/1 currently copies all pages if that what you meant.
>>
>
> Small correction: RAID5 and RAID6 copy all pages.
> RAID1 and RAID10 do not.
>
> If the incoming bios had nicely aligned pages which were somehow flagged to
> say that they would not change until the request completed, then it should be
> trivial to avoid that copy.
Lustre has a patch to that effect that we've been carrying for several years.
It avoids copying of the pages submitted to the RAID5/6 layer, and provides
a significant improvement in performance and efficiency.
A version of the patches for RHEL6 is available at:
http://review.whamcloud.com/1142
though I don't know how close it is to working with the latest kernel.
Cheers, Andreas
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