swidth with mdadm and RAID6

Steve Cousins
2006-09-15T22:07:46Z

I have a RAID6 array of 11 500 GB drives using mdadm. There is one
hot-spare so the number of data drives is 8. I used mkfs.xfs with
defaults to create the file system and it seemed to pick up the chunk size
I used correctly (64K) but I think it got the swidth wrong. Here is what
xfs_info says:

===========================================================================
meta-data=/dev/md0 isize=256 agcount=32, agsize=30524160
blks
= sectsz=4096 attr=0
data = bsize=4096 blocks=976772992, imaxpct=25
= sunit=16 swidth=144 blks, unwritten=1
naming =version 2 bsize=4096
log =internal bsize=4096 blocks=32768, version=2
= sectsz=4096 sunit=1 blks
realtime =none extsz=589824 blocks=0, rtextents=0
===========================================================================

So, sunit*bsize=64K, but swidth=144 and swidth/sunit=9 so it looks like it
thought there were 9 data drives instead of 8.

Am I diagnosing this correctly? Should I recreate the array and
explicitly set sunit=16 and swidth=128?

Thanks for your help.

Steve
______________________________________________________________________
Steve Cousins, Ocean Modeling Group Email: cousins@umit.maine.edu
Marine Sciences, 452 Aubert Hall http://rocky.umeoce.maine.edu
Univ. of Maine, Orono, ME 04469 Phone: (207) 581-4302