Hi Luke, On Tue, 2005-11-15 at 10:42 -0800, Luke Lonergan wrote: > With RAID5, it could matter a lot what block size you run your “dd > bigfile” test with. You should run “dd if=/dev/zero of=bigfile bs=8k > count=500000” for a 2GB main memory machine, multiply the count by > (<your mem>/2GB). If I understand correctly (I have 4GB ram): jkr@Panoramix:~/tmp$ dd if=/dev/zero of=bigfile bs=8k count=1000000 1000000+0 records in 1000000+0 records out 8192000000 bytes transferred in 304.085269 seconds (26939812 bytes/sec) Which looks suspicious: 26308 MB/sec??? > It is very important with the 3Ware cards to match the driver to the > firmware revision. OK, I am running 1 driver behind the firmware. > I did notice that changing the I/O scheduler's nr_request from > the > default 128 to 1024 or even 4096 made a remarkable performance > improvement. I suspect that experimenting with other I/O > schedululers > could improve performance. But it is hard to find any useful > documentation about I/O schedulers. > > You could try deadline, there’s no harm, but I’ve found that when you > reach the point of experimenting with schedulers, you are probably not > addressing the real problem. It depends. I/O Schedulers (I assume) have a purpose: some schedulers should be more appropriate for some circumstances. And maybe my specific circumstances (converting a database with *many updates*) is a specific circumstance. I really don't know.... > On a 3Ware 9500 with HW RAID5 and 4 or more disks I think you should > get 100MB/s write rate, which is double what Postgres can use. We > find that Postgres, even with fsync=false, will only run at a net COPY > speed of about 8-12 MB/s, where 12 is the Bizgres number. 8.1 might > do 10. But to get the 10 or 12, the WAL writing and other writing is > about 4-5X more than the net write speed, or the speed at which the > input file is parsed and read into the database. As I have an (almost) seperate WAL disk: iostat does not show any significant writing on the WAL disk.... > So, if you can get your “dd bigfile” test to write data at 50MB/s+ > with a blocksize of 8KB, you should be doing well enough. See above. > Incidentally, we also find that using the XFS filesystem and setting > the readahead to 8MB or more is extremely beneficial for performance > with the 3Ware cards (and with others, but especially for the older > 3Ware cards). I don't have problems with my read performance but *only* with my *update* performance (and not even insert performance). But than again I am not the only one with these problems: http://www.issociate.de/board/goto/894541/3ware_+_RAID5_ +_xfs_performance.html#msg_894541 http://lkml.org/lkml/2005/4/20/110 http://seclists.org/lists/linux-kernel/2005/Oct/1171.html I am happy to share the tables against which I am running my checks.... -- Groeten, Joost Kraaijeveld Askesis B.V. Molukkenstraat 14 6524NB Nijmegen tel: 024-3888063 / 06-51855277 fax: 024-3608416 e-mail: J.Kraaijeveld@xxxxxxxxxx web: www.askesis.nl ---------------------------(end of broadcast)--------------------------- TIP 4: Have you searched our list archives? http://archives.postgresql.org
