Re: H800 + md1200 Performance problem

Raid controller issue or driver problem was the first problem that I
studied.
I installed Centos 5.4 al the beginning, but I had performance problems,
and I contacted Dell support... but Centos is not support by Dell... Then I
installed Redhat 6 and we contact Dell with same problem.
Dell say that all is right and that this is a software problem.
I have installed Centos 5.4, 6.2 and Redhat 6 with similar result, I think
that not is driver problem (megasas-raid kernel module).
I will check kernel updates...
Thanks!

PS. lately I'm pretty disappointed with the quality of the DELL components, is
not the first problem we have with hardware in new machines.

El 4 de abril de 2012 19:16, Merlin Moncure <mmoncure(at)gmail(dot)com> escribió:

> On Wed, Apr 4, 2012 at 4:42 AM, Cesar Martin <cmartinp(at)gmail(dot)com> wrote:
> > Hello,
> >
> > Yesterday I changed the kernel setting, that said
> > Scott, vm.zone_reclaim_mode = 0. I have done new benchmarks and I have
> > noticed changes at least in Postgres:
> >
> > First exec:
> > EXPLAIN ANALYZE SELECT * from company_news_internet_201111;
> > QUERY
> PLAN
> >
> >
> --------------------------------------------------------------------------------------------------------------------------------------------
> > Seq Scan on company_news_internet_201111 (cost=0.00..369577.79
> > rows=6765779 width=323) (actual time=0.020..7984.707 rows=6765779
> loops=1)
> > Total runtime: 12699.008 ms
> > (2 filas)
> >
> > Second:
> > EXPLAIN ANALYZE SELECT * from company_news_internet_201111;
> > QUERY
> PLAN
> >
> >
> --------------------------------------------------------------------------------------------------------------------------------------------
> > Seq Scan on company_news_internet_201111 (cost=0.00..369577.79
> > rows=6765779 width=323) (actual time=0.023..1767.440 rows=6765779
> loops=1)
> > Total runtime: 2696.901 ms
> >
> > It seems that now data is being cached right...
> >
> > The large query in first exec takes 80 seconds and in second exec takes
> > around 23 seconds. This is not spectacular but is better than yesterday.
> >
> > Furthermore the results of dd are strange:
> >
> > dd if=/dev/zero of=/vol02/bonnie/DD bs=8M count=16384
> > 16384+0 records in
> > 16384+0 records out
> > 137438953472 bytes (137 GB) copied, 803,738 s, 171 MB/s
> >
> > 171 MB/s I think is bad value for 12 SAS RAID10... And when I execute
> iostat
> > during the dd execution i obtain results like:
> > sdc 1514,62 0,01 108,58 11 117765
> > sdc 3705,50 0,01 316,62 0 633
> > sdc 2,00 0,00 0,05 0 0
> > sdc 920,00 0,00 63,49 0 126
> > sdc 8322,50 0,03 712,00 0 1424
> > sdc 6662,50 0,02 568,53 0 1137
> > sdc 0,00 0,00 0,00 0 0
> > sdc 1,50 0,00 0,04 0 0
> > sdc 6413,00 0,01 412,28 0 824
> > sdc 13107,50 0,03 867,94 0 1735
> > sdc 0,00 0,00 0,00 0 0
> > sdc 1,50 0,00 0,03 0 0
> > sdc 9719,00 0,03 815,49 0 1630
> > sdc 2817,50 0,01 272,51 0 545
> > sdc 1,50 0,00 0,05 0 0
> > sdc 1181,00 0,00 71,49 0 142
> > sdc 7225,00 0,01 362,56 0 725
> > sdc 2973,50 0,01 269,97 0 539
> >
> > I don't understand why MB_wrtn/s go from 0 to near 800MB/s constantly
> during
> > execution.
>
> This is looking more and more like a a raid controller issue. ISTM
> it's bucking the cache, filling it up and flushing it synchronously.
> your read results are ok but not what they should be IMO. Maybe it's
> an environmental issue or the card is just a straight up lemon (no
> surprise in the dell line). Are you using standard drivers, and have
> you checked for updates? Have you considered contacting dell support?
>
> merlin
>

--
César Martín Pérez
cmartinp(at)gmail(dot)com