Messages in this thread | | | Date | Tue, 25 Mar 2008 18:37:06 -0400 | From | Bill Davidsen <> | Subject | Re: RAID-1 performance under 2.4 and 2.6 |
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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... ? :) > Unfortunately this shows the same trend as kernel compile, small database operations, etc. If you are using a journaling filesystem on 2.6 and not 2.4 be sure you have the filesystem mounted "noatime" or retest with a non-journaled f/s. If you are running LVM in the test all bets are off as there are alignment issues (see linux-raid archives) to consider.
But the trend has unfortunately been slower, and responses demanding you use another benchmark, saying that kernel compile is not a benchmark, suggesting use of postgress or oracle instead of MySQL, etc, are seen.
I wish it were not so, there seems to be more effort going to explaining results than improving them. That said, tuning the location of the f/s, the stride, chunk size, etc, can improve things, and there are patches available for test (linux-raid again) which will address some of this fairly soon.
-- Bill Davidsen <davidsen@tmr.com> "We have more to fear from the bungling of the incompetent than from the machinations of the wicked." - from Slashdot
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