27.08.2012 14:43, Sašo Kiselkov пишет:

Is there any way to disable ARC for testing and leave prefetch enabled?


No. The reason is quite simply because prefetch is a mechanism separate
from your direct application's read requests. Prefetch runs on ahead of
your anticipated read requests and places blocks it expects you'll need
in the ARC, so obviously by disabling the ARC, you've disabled prefetch
as well.

You can get around the problem by exporting and importing the dataset
between testing runs, which will clear the ARC, so do:

# dd if=/dev/zero of=testfile bs=1024k count=10000
# zpool export sas1
# zpool import sas1
# dd if=testfile of=/dev/null bs=1024k

Thank you very much, Sašo.
Now i see hardware works without problem.

I create another 10-disks pair of mirrors zpool for testing:

root@atom:/# zpool export sas2 ; zpool import sas2
root@atom:/# readspeed /sas2/5g
5120+0 records in
5120+0 records out
5368709120 bytes (5.4 GB) copied, 5.73728 s, 936 MB/s
root@atom:/# zpool export sas2 ; zpool import sas2
root@atom:/# readspeed /sas2/5g
5120+0 records in
5120+0 records out
5368709120 bytes (5.4 GB) copied, 5.63869 s, 952 MB/s



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