Re: U320 Large Array Performance

["Rick Smith" <rgsmith72@xxxxxxxxxxx>]

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


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