Messages in this thread | | | Date | Wed, 26 Mar 2008 08:15:15 +0100 | From | "Bart Van Assche" <> | Subject | Re: RAID-1 performance under 2.4 and 2.6 |
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On Tue, Mar 25, 2008 at 11:00 PM, Chris Snook <csnook@redhat.com> wrote: > Emmanuel Florac wrote: > > I post there because I couldn't find any information about this > > elsewhere : on the same hardware ( Athlon X2 3500+, 512MB RAM, 2x400 GB > > Hitachi SATA2 hard drives ) the 2.4 Linux software RAID-1 (tested 2.4.32 > > and 2.4.36.2, slightly patched to recognize the hardware :p) is way > > faster than 2.6 ( tested 2.6.17.13, 2.6.18.8, 2.6.22.16, 2.6.24.3) > > especially for writes. I actually made the test on several different > > machines (same hard drives though) and it remained consistent across > > the board, with /mountpoint a software RAID-1. > > Actually checking disk activity with iostat or vmstat shows clearly a > > cache effect much more pronounced on 2.4 (i.e. writing goes on much > > longer in the background) but it doesn't really account for the > > difference. I've also tested it thru NFS from another machine (Giga > > ethernet network): > > > > dd if=/dev/zero of=/mountpoint/testfile bs=1M count=1024 > > > > kernel 2.4 2.6 2.4 thru NFS 2.6 thru NFS > > > > write 90 MB/s 65 MB/s 70 MB/s 45 MB/s > > read 90 MB/s 80 MB/s 75 MB/s 65 MB/s > > > > Duh. That's terrible. Does it mean I should stick to (heavily > > patched...) 2.4 for my file servers or... ? :) > > It means you shouldn't use dd as a benchmark.
If you want to benchmark write speed, you should add oflag=direct,dsync to the dd command line. For benchmarking read speed you should specify iflag=direct. Or, even better, you can use xdd with the flags -dio -processlock.
Bart.
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