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U320 Large Array Performance

To: linux-xfs@xxxxxxxxxxx
Subject: U320 Large Array Performance
From: "Rick Smith" <rgsmith72@xxxxxxxxxxx>
Date: Tue, 04 Feb 2003 14:09:40 -0800
Sender: linux-xfs-bounce@xxxxxxxxxxx
I am constructing a large, high performance U320 raid0 array with XFS using the 2.4.20-rc1-xfs kernel and linux software raid. I am pleased with the performance, but it seems that when I exceed 14 disks total in the single raid0 array, performance becomes erratic. With 14 disks and under, the extents are laid out nicely in incrementing order very close to each other (according to xfs_bmap) and I can get very large MB/s numbers using 4 U320 SCSI channels and 73GB disks. However, with 15+ disks, I am seeing large, erratic gaps in the extents, which is seriously affecting read/write performance. I don't exceed 5 drives per channel, and the problem seems to exist no matter what SCSI configuration that I use. I have tried various numbers of channels and disks per channel, but the problem remains when I exceed 14 disks. Currently the read performance for 15 disks is about half the read performance for 14 disks in the array. Other filesystems tested (reiserfs and ext2/3) do not seem to suffer from this problem, but they also don't produce the awesome speed that the XFS filesystem does. I plan on experimenting with the latest 2.4 and 2.5 versions of the XFS kernel as soon as I can get a good copy from CVS.
   Any help is appreciated. Thanks.

Rick Smith








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