On Tue, 26 Feb 2013, hagai wrote:

for what is worth..
I had the same problem and found the answer here -

Given enough sequential I/O requests, zfs mirrors behave every much like RAID-0 for reads. Sequential prefetch is very important in order to avoid the latencies.

While this script may not work perfectly as is for FreeBSD, it was very good at discovering a zfs performance bug (since corrected) and is still an interesting exercise for zfs to see how ZFS ARC caching helps for re-reads. See "http://www.simplesystems.org/users/bfriesen/zfs-discuss/zfs-cache-test.ksh";. The script will exercise an initial uncached read from disks, and then a (hopefully) cached re-read from disks. I think that it serves as a useful benchmark.

Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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