Peter, On 1/6/06 2:59 PM, "peter royal" <peter.royal@xxxxxxxxx> wrote: > I have experimented with having all 8 disks in a single RAID0 set, a > single RAID10 set, and currently 4 RAID0 sets of 2 disks each. There > hasn't been an appreciable difference in the overall performance of > my test suite (which randomly generates queries like the samples > below as well as a few other types. this problem manifests itself on > other queries in the test suite as well). Have you tested the underlying filesystem for it's performance? Run this: time bash -c 'dd if=/dev/zero of=/my_file_system/bigfile bs=8k count=<your_memory_size_in_GB * 250000> && sync' Then run this: time dd if=/my_file_system/bigfile bs=8k of=/dev/null And report the times here please. With your 8 disks in any of the RAID0 configurations you describe, you should be getting 480MB/s. In the RAID10 configuration you should get 240. Note that ext3 will not go faster than about 300MB/s in our experience. You should use xfs, which will run *much* faster. You should also experiment with using larger readahead, which you can implement like this: blockdev --setra 16384 /dev/<my_block_device> E.g. "blockdev --setra 16384 /dev/sda" This will set the readahead of Linux block device reads to 16MB. Using 3Ware's newest controllers we have seen 500MB/s + on 8 disk drives in RAID0 on CentOS 4.1 with xfs. Note that you will need to run the "CentOS unsupported kernel" to get xfs. > So, my question is, is there anything I can do to boost performance > with what I've got, or am I in a position where the only 'fix' is > more faster disks? I can't think of any schema/index changes that > would help, since everything looks pretty optimal from the 'explain > analyze' output. I'd like to get a 10x improvement when querying from > the 'cold' state.
