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Re: H800 + md1200 Performance problem

From: Cesar Martin <cmartinp(at)gmail(dot)com>
To: Merlin Moncure <mmoncure(at)gmail(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: H800 + md1200 Performance problem
Date: 2012-04-04 18:46:33
Message-ID: CAMAsR=7Xkzcr-G_NO-Jn2yTa+BSayuMMK7Gv7diXDNcC3WNVUw@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
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

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Subject: Re: H800 + md1200 Performance problem
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