Justin Piszcz wrote:

Btw, max sectors did improve my performance a little bit but
stripe_cache+read_ahead were the main optimizations that made everything
go faster by about ~1.5x.   I have individual bonnie++ benchmarks of
[only] the max_sector_kb tests as well, it improved the times from
8min/bonnie run -> 7min 11 seconds or so, see below and then after that is
what you requested.

# echo 3 > /proc/sys/vm/drop_caches
# dd if=/dev/md3 of=/dev/null bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 399.352 seconds, 26.9 MB/s
# for i in sde sdg sdi sdk; do   echo 192 >
/sys/block/"$i"/queue/max_sectors_kb;   echo "Set
/sys/block/"$i"/queue/max_sectors_kb to 192kb"; done
Set /sys/block/sde/queue/max_sectors_kb to 192kb
Set /sys/block/sdg/queue/max_sectors_kb to 192kb
Set /sys/block/sdi/queue/max_sectors_kb to 192kb
Set /sys/block/sdk/queue/max_sectors_kb to 192kb
# echo 3 > /proc/sys/vm/drop_caches
# dd if=/dev/md3 of=/dev/null bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 398.069 seconds, 27.0 MB/s

Awful performance with your numbers/drop_caches settings.. !

Can you repeat with /dev/sda only?

With fresh reboot to shell, then:
$ cat /sys/block/sda/queue/max_sectors_kb
$ echo 3 > /proc/sys/vm/drop_caches
$ dd if=/dev/sda of=/dev/null bs=1M count=10240

$ echo 192 > /sys/block/sda/queue/max_sectors_kb
$ echo 3 > /proc/sys/vm/drop_caches
$ dd if=/dev/sda of=/dev/null bs=1M count=10240

$ echo 128 > /sys/block/sda/queue/max_sectors_kb
$ echo 3 > /proc/sys/vm/drop_caches
$ dd if=/dev/sda of=/dev/null bs=1M count=10240

What were your tests designed to show?

A problem with the block-io.


Thanks!

--
Al