Re: Filesystem benchmarking for pg 8.3.3 server

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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