Re: Filesystem benchmarking for pg 8.3.3 server

But random writes should be faster on a RAID10 as it doesn't need to
calculate parity. That is why people suggest RAID 10 for datases,
correct?

I can understand that RAID5 can be faster with sequential writes.

//Henke

8 aug 2008 kl. 16.53 skrev Luke Lonergan:

> Your expected write speed on a 4 drive RAID10 is two drives worth,
> probably 160 MB/s, depending on the generation of drives.
>
> The expect write speed for a 6 drive RAID5 is 5 drives worth, or
> about 400 MB/s, sans the RAID5 parity overhead.
>
> - Luke
>
> ----- Original Message -----
> From: pgsql-performance-owner(at)postgresql(dot)org <pgsql-performance-owner(at)postgresql(dot)org
> >
> To: pgsql-performance(at)postgresql(dot)org <pgsql-
> performance(at)postgresql(dot)org>
> Sent: Fri Aug 08 10:23:55 2008
> Subject: [PERFORM] Filesystem benchmarking for pg 8.3.3 server
>
> Hello list,
>
> I have a server with a direct attached storage containing 4 15k SAS
> drives and 6 standard SATA drives.
> The server is a quad core xeon with 16GB ram.
> Both server and DAS has dual PERC/6E raid controllers with 512 MB BBU
>
> There is 2 raid set configured.
> One RAID 10 containing 4 SAS disks
> One RAID 5 containing 6 SATA disks
>
> There is one partition per RAID set with ext2 filesystem.
>
> I ran the following iozone test which I stole from Joshua Drake's test
> at
> http://www.commandprompt.com/blogs/joshua_drake/2008/04/is_that_performance_i_smell_ext2_vs_ext3_on_50_spindles_testing_for_postgresql/
>
> I ran this test against the RAID 5 SATA partition
>
> #iozone -e -i0 -i1 -i2 -i8 -t1 -s 1000m -r 8k -+u
>
> With these random write results
>
> Children see throughput for 1 random writers = 168647.33
> KB/sec
> Parent sees throughput for 1 random writers = 168413.61
> KB/sec
> Min throughput per process = 168647.33
> KB/sec
> Max throughput per process = 168647.33
> KB/sec
> Avg throughput per process = 168647.33
> KB/sec
> Min xfer = 1024000.00
> KB
> CPU utilization: Wall time 6.072 CPU time 0.540
> CPU
> utilization 8.89 %
>
> Almost 170 MB/sek. Not bad for 6 standard SATA drives.
>
> Then I ran the same thing against the RAID 10 SAS partition
>
> Children see throughput for 1 random writers = 68816.25
> KB/sec
> Parent sees throughput for 1 random writers = 68767.90
> KB/sec
> Min throughput per process = 68816.25
> KB/sec
> Max throughput per process = 68816.25
> KB/sec
> Avg throughput per process = 68816.25
> KB/sec
> Min xfer = 1024000.00
> KB
> CPU utilization: Wall time 14.880 CPU time 0.520
> CPU
> utilization 3.49 %
>
> What only 70 MB/sek?
>
> Is it possible that the 2 more spindles for the SATA drives makes that
> partition soooo much faster? Even though the disks and the RAID
> configuration should be slower?
> It feels like there is something fishy going on. Maybe the RAID 10
> implementation on the PERC/6e is crap?
>
> Any pointers, suggestion, ideas?
>
> I'm going to change the RAID 10 to a RAID 5 and test again and see
> what happens.
>
> Cheers,
> Henke
>
>
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