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Hello All,
I am wondering if anyone can offer any insight into a problem I have been
seeing with XFS included in the 2.4.27 kernel. I am seeing a huge difference
between a raw device (/dev/md0) read and a filesystem read when reading from
an array that is capable of >500 MBytes/sec. The reads and writes are
sequential, both on the raw disk device and XFS filesystem (using sequential
files).
Here is an example of what we normally see on a fairly slow array:
RAW PERFORMANCE
Read Average : 212.674 MB/SEC over 1000 frames
Write Average: 234.769 MB/SEC over 1000 frames
FS PERFORMANCE
Read Average : 148.125 MB/SEC over 1000 frames
Write Average: 286.031 MB/SEC over 1000 frames
Now here is the problem I am seeing on a fast array:
RAW PERFORMANCE
Read Average : 594.965 MB/SEC over 1000 frames
Write Average: 350.604 MB/SEC over 1000 frames
FS PERFORMANCE
Read Average : 67.280 MB/SEC over 1000 frames
Write Average: 305.363 MB/SEC over 1000 frames
I have seen similar results on two separate arrays, one a software raid of
dual U320 arrays, the other is a software raid of dual 2G fibre w/ 16 disks.
I don't suspect it is a problem with the physical interfaces, as I am seeing
the same issue on multiple technologies. Also, I have pretty much ruled out
a problem with Linux software raid as we are getting expected performance
from the raw /dev/md0 device. That is not to say that it couldn't very well
be a nasty interaction between software raid and XFS.
Thanks much!
Jason
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Jason Howard
Professional:
SpectSoft, LLC
593 Hi-Tech Pkwy, Suite B
Oakdale, CA 95361, USA
http://www.spectsoft.com
jason a-t spectsoft.com
Phone: +1.209.847.7812
Fax: +1.209.847.7859
Personal:
http://www.psinux.org
jason a-t psinux.org
Cell: +1.209.968.1289
Text Message: jasonsphone a-t psinux.org
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