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Re: U320 Large Array Performance

To: lord@xxxxxxx
Subject: Re: U320 Large Array Performance
From: "Rick Smith" <rgsmith72@xxxxxxxxxxx>
Date: Tue, 04 Feb 2003 14:47:34 -0800
Cc: linux-xfs@xxxxxxxxxxx
Sender: linux-xfs-bounce@xxxxxxxxxxx
Here is the output from xfs_info, please excuse the formatting. I am using a chunk size of 4K in the raid. Larger sizes seem to degrade performance. Thanks for your help.

With 14 disks in the array:
meta-data=/test isize=256 agcount=240, agsize=1048576 blks data = bsize=4096 blocks=251392736, imaxpct=25 = sunit=1 swidth=14 blks, unwritten=1
naming   =version 2             bsize=4096
log      =external                    bsize=4096   blocks=32768 version=1
                       =                       sunit=0 blks
realtime =none                     extsz=57344  blocks=0, rtextents=0

With 15 disks in the array
meta-data=/test isize=256 agcount=257, agsize=1048576 blks data = bsize=4096 blocks=269349360, imaxpct=25 = sunit=1 swidth=15 blks, unwritten=1
naming   =version 2             bsize=4096
log      =external                    bsize=4096   blocks=32768 version=1
                      =                        sunit=0 blks
realtime =none                     extsz=61440  blocks=0, rtextents=0

From: Steve Lord <lord@xxxxxxx>
To: Rick Smith <rgsmith72@xxxxxxxxxxx>
CC: linux-xfs@xxxxxxxxxxx
Subject: Re: U320 Large Array Performance
Date: 04 Feb 2003 16:16:05 -0600

On Tue, 2003-02-04 at 16:09, Rick Smith wrote:
> 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.

Sounds like you need to play with mkfs options on XFS. Can you send
the output of xfs_info /mnt where /mnt is the mounted filesystem.



Steve Lord                                      voice: +1-651-683-3511
Principal Engineer, Filesystem Software         email: lord@xxxxxxx

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