[arch-general] mdadm: RAID-5 performance sucks

[Chris Down]

On 10 April 2013 00:16, Karol Babioch <karol at babioch.de> wrote:

> Hi,
>
> I've got four HDDs and added them into a RAID-5 array, which basically
> works just fine. However the performance sucks quite hard. I get only
> about 70 MB/s when it comes down to reading and writing speeds of about
> 35 MB/s.
>
> The hardware itself is quite decent: Intel Xeon E31260L, 8 GB RAM and
> four Samsung HD204UI's. With the same setup and a Ubuntu live
> environment I get about 270 MB/s reading speed and 130 MB/s writing speed.
>
> Therefore there must be a fundamental difference. I've compared various
> values from sysctl between both environments and set them accordingly,
> but to no availability.
>
> Anyone else experiencing the same issues and/or can you point me in the
> right direction?
>
> At least I would like to saturate my Gigabit Ethernet connection.
>
> Best regards,
> Karol Babioch
>
>
I assume you're using Linux software RAID, although you don't mention. I've
experienced this when using RAID6 and a suboptimal stripe cache size. Try
tinkering with /sys/block/mdX/md/stripe_cache_size. In my case adjusting it
to 8192 increased read and write speeds dramatically.

Chris