[OpenIndiana-discuss] [zfs-discuss] slow speed problem with a new SAS shelf

[Sašo Kiselkov]

On 08/27/2012 10:37 AM, Yuri Vorobyev wrote:
> 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

Cheers,
--
Saso