I've set up an software RAID-60 array composed of 7 software RAID6's,
each with 32k chunks, 18 devices total (16 data, 2 parity), and in
theory appropriate setup parameters according to a nice white paper
written by Christoph and presented this last summer at LinuxCon.
My question is, if the mdraid and XFS are all configured properly,
would I expect to see any read operations when doing a write-only
test? I would have assumed that I would not, since XFS should write
stripe-aligned sets of data, and in theory nothing needs to be read
(no read-modify-write going on, I would think).
The performance is great, but I'm wondering if I need to keep looking.
Thanks,
Paul Anderson
Here's the details for kernel 2.6.38.5:
mdadm --detail /dev/md0 (md1, md2, md3, md4, md5, and md6 all the same)
/dev/md0:
Version : 01.02
Creation Time : Fri Dec 2 14:54:23 2011
Raid Level : raid6
Array Size : 31256214528 (29808.25 GiB 32006.36 GB)
Used Dev Size : 3907026816 (3726.03 GiB 4000.80 GB)
Raid Devices : 18
Total Devices : 18
Preferred Minor : 0
Persistence : Superblock is persistent
Update Time : Mon Dec 5 13:38:52 2011
State : clean
Active Devices : 18
Working Devices : 18
Failed Devices : 0
Spare Devices : 0
Chunk Size : 32K
/dev/md8 is the RAID0 that concatenates the above RAID6's, making a
single RAID60:
mdadm --detail /dev/md8
/dev/md8:
Version : 01.02
Creation Time : Fri Dec 2 14:55:36 2011
Raid Level : raid0
Array Size : 218793480192 (208657.73 GiB 224044.52 GB)
Raid Devices : 7
Total Devices : 7
Preferred Minor : 8
Persistence : Superblock is persistent
Update Time : Fri Dec 2 14:55:36 2011
State : clean
Active Devices : 7
Working Devices : 7
Failed Devices : 0
Spare Devices : 0
Chunk Size : 4096K (this is what the RAID0 container thinks, but
I ignore it for xfs)
xfs_info /exports/
meta-data=/dev/md8 isize=256 agcount=204, agsize=268435448 blks
= sectsz=512 attr=2
data = bsize=4096 blocks=54698370048, imaxpct=1
= sunit=8 swidth=1024 blks
naming =version 2 bsize=4096 ascii-ci=0
log =internal bsize=4096 blocks=521728, version=2
= sectsz=512 sunit=8 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
I made the filesystem like this:
mkfs.xfs -L $(hostname) -l su=32768 -d su=32768,sw=128 /dev/md8
mount options: inode64,largeio,swalloc,delaylog,logbsize=256k,logbufs=8,noatime,nodiratime
I intended to make it with an external log, but forgot.
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