Hi,
during some xfs tuning tests I discovered the following phenomenon.
Maybe someone can explain it to me:
Bonnie++ Reading with getc()... hits exactly an almost constant
65536 kbyte/s with only ~15% IO usage.
iostat and bonnie output can be found under:
http://alexander.liemen.net/bonnie.txt
sdb is a 14 disk RAID10 (128kb stripe) 2.8Tbyte XFS Volume with an
external log (128Mb) on sda7 (Raid1)
mount options are:
noatime,nodiratime,logbufs=8,ihashsize=65536,logdev=/dev/sda7
mkfs:
mkfs.xfs -f -d sunit=256,swidth=1792 -l
version=2,size=128m,logdev=/dev/sda7 /dev/sdb
scheduler: deadline
system:
- debian testing 2.6.15-1-amd64-k8-smp
- dual opteron 275-285 (both tested)
- 16gb ram
- areca pci-x 1160 controller 1gb cache v1.41 firmware
- WD400YR disks
CPU usage is 100% (on one of the cpus) but i don't think that's the
limiting factor since it hits that 16bit value absolut constantly.
I have also tested it with exactly the same server but faster CPUs and
it's hitting the same barrier + tested it with no mkfs.xfs options + no
mount options on a second identical server. Same problem.
Intelligent reading is way above with 350+ Mb/s (check bonnie.txt)
Anyone got an idea why it is hitting that 16bit value / barrier?
Also of interest would be why the random seeks are so bad.
Thanks a lot
Alex
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