Re: raid10 centos5 vs. centos6 300% worse random write performance

Mikael Abrahamsson <swmike <at> swm.pp.se> writes:

On Thu, 25 Jul 2013, Wes wrote:

quoted

Why raid10 driver from Centos 6 has a 300% slower random write performance
(random read stays the same) than Centos 5?

Please share your ideas.

... 
Does seekmark use barriers to assure that data has actually been written? 
In that case it could be that 2.6.18 has different behaviour from 2.6.32 
when it comes to barriers and that explains the speed difference.

I also made random write tests with raid1 and these return the same results
on centos 5 and 6 (+/- 1%)
thread 1 completed, time: 85.34, 11.72 seeks/sec, 85.3ms per request
...
93.28 total seeks per sec, 11.66 WRITE seeks per sec per thread

And raid10 random write speed on centos 5 is twice as much as above - this
is expected as there are 4 spindles.
But centos6's raid10 (4 spindles) random write speed (~120ms/req) is even
slower than 2 spindle raid1 (~80ms/req).
This experiment seems to narrow the problem down to raid10.