Re: Software RAID checksum performance on 24 disks not even close to kernel reported

[Ole Tange <ole@xxxxxxxx>]

On Tue, Jun 5, 2012 at 3:09 PM, Peter Grandi <pg@xxxxxxxxxxxxxxxxxxxx> wrote:
> [ ... ]
>
>>> Good call. But the resync is done before the mkfs.xfs is finished, so
>>> the time of the copying is not affected by resync.
>>>
>>> I re-tested with --assume-clean and as expected it has no impact.
>
>>    Wanna try CONFIG_MULTICORE_RAID456? :-)
>
> That would be intreresting, but the original post reports over
> 6GB/s for pure checksumming, and around 400MB/s actual transfer
> rate. In theory there is no need here for multihreading. There
> may something else going on :-).

I have the feeling that some of you have not experienced md0_raid6
taking up 100% CPU of a single core. If you have not, please run the
test on http://oletange.blogspot.dk/2012/05/software-raid-performance-on-24-disks.html

The test requires 10 GB RAM, atleast 2 CPU cores, and takes less than
3 minutes to run.

See if you can reproduce the CPU usage, and post your results along
with the reported checksumming speed reported by the kernel.


/Ole
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