Re: RAID-1 performance under 2.4 and 2.6
From: Bill Davidsen
Date: Tue Mar 25 2008 - 18:47:04 EST
Chris Snook 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.
What do you use as a benchmark for writing large sequential files or
reading them, and why is it better than dd at modeling programs which
read or write in a similar fashion?
Media programs often do data access in just this fashion, multi-channel
video capture, streaming video servers, and similar.
--
Bill Davidsen <davidsen@xxxxxxx>
"We have more to fear from the bungling of the incompetent than from
the machinations of the wicked." - from Slashdot
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