On Jan 9, 2006, at 2:01 PM, Luke Lonergan wrote:
Peter, On 1/9/06 9:23 AM, "peter royal" <peter.royal@xxxxxxxxx> wrote:This is a 2-disk RAID0Your 2-disk results look fine - what about your 8-disk results?
after some further research the 2-disk RAID0 numbers are not bad.I have a single drive of the same type hooked up to the SATA2 port on the motherboard to boot from, and its performance numbers are (linux 2.6.15, ext3):
[root@bigboy ~]# time bash -c 'dd if=/dev/zero of=/tmp/bigfile bs=8k count=1000000 && sync'
1000000+0 records in 1000000+0 records out real 4m55.032s user 0m0.256s sys 0m47.299s [root@bigboy ~]# time dd if=/tmp/bigfile bs=8k of=/dev/null 1000000+0 records in 1000000+0 records out real 3m27.229s user 0m0.156s sys 0m13.377s so, there is a clear advantage to RAID over a single drive. now, some stats in a 8-disk configuration: 8-disk RAID0, ext3, 16k read-ahead[root@bigboy /opt/pgdata]# time bash -c 'dd if=/dev/zero of=/opt/ pgdata/bigfile bs=8k count=1000000 && sync'
1000000+0 records in 1000000+0 records out real 0m53.030s user 0m0.204s sys 0m42.015s[root@bigboy /opt/pgdata]# time dd if=/opt/pgdata/bigfile bs=8k of=/ dev/null
1000000+0 records in 1000000+0 records out real 0m23.232s user 0m0.144s sys 0m13.213s 8-disk RAID0, xfs, 16k read-ahead[root@bigboy /opt/pgdata]# time bash -c 'dd if=/dev/zero of=/opt/ pgdata/bigfile bs=8k count=1000000 && sync'
1000000+0 records in 1000000+0 records out real 0m32.177s user 0m0.212s sys 0m21.277s[root@bigboy /opt/pgdata]# time dd if=/opt/pgdata/bigfile bs=8k of=/ dev/null
1000000+0 records in 1000000+0 records out real 0m21.814s user 0m0.172s sys 0m13.881s... WOW.. highly impressed with the XFS write speed! going to stick with that!
Overall, I got a 50% boost in the overall speed of my test suite by using XFS and the 16k read-ahead.
Given that you want to run in production with RAID10, the most you should expect is 2x the 2-disk results using all 8 of your disks. If you want thebest rate for production while preserving data integrity, I recommend running your Areca in RAID5, in which case you should expect 3.5x your2-disk results (7 drives). You can assume you'll get that if you use XFS +readahead. OTOH - I'd like to see your test results anyway :-)
I've been avoiding RAID5 after reading how performance drops when a drive is out/rebuilding. The performance benefit will outweigh the cost I think.
Thanks for the help! -pete -- (peter.royal|osi)@pobox.com - http://fotap.org/~osi
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