Re: How to setup disk spindles for best performance

On Thu, 21 Aug 2008, Christiaan Willemsen wrote:

> Anyway, I'm going to return the controller, because it
> does not scale very well with more that 4 disks in raid 10. Bandwidth is
> limited to 350MB/sec, and IOPS scale badly with extra disks...

How did you determine that upper limit? Usually it takes multiple
benchmark processes running at once in order to get more than 350MB/s out
of a controller. For example, if you look carefully at the end of
http://www.commandprompt.com/blogs/joshua_drake/2008/04/is_that_performance_i_smell_ext2_vs_ext3_on_50_spindles_testing_for_postgresql/
you can see that Joshua had to throw 8 threads at the disks in order to
reach maximum bandwidth.

> The idea for xlog + os on 4 disk raid 10 and the rest for the data sound
> good

I would just use a RAID1 pair for the OS, another pair for the xlog, and
throw all the other disks into a big 0+1 set. There is some value to
separating the WAL from the OS disks, from both the performance and the
management perspectives. It's nice to be able to monitor the xlog write
bandwidth rate under load easily for example.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD