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@xxxxxxxxxxxxx http://www.gregsmith.com Baltimore, MD
