Quoting Bob Friesenhahn <bfrie...@simple.dallas.tx.us>:
On Mon, 31 Aug 2009, en...@businessgrade.com wrote:
Hi. I've been doing some simple read/write tests using filebench on
a mirrored pool. Essentially, I've been scaling up the number of
disks in the pool before each test between 4, 8 and 12. I've
noticed that for individual disks, ZFS write performance scales
very well between 4, 8 and 12 disks. This may be due to the fact
that I'm using a SSD as a logging device. But I'm seeing individual
disk performance drop by as much as 14MB per disk between 4 and 12
disks. Across the entire pool that means I've lost 168MB of raw
throughput just by adding two mirror sets. I'm curious to know if
there are any dials I can turn to improve this. System details are
below:
Sun is currently working on several prefetch bugs (complete loss of
prefetch & insufficient prefetch) which have been identified. Perhaps
you were not on this list in July when a huge amount of discussion
traffic was dominated by the topic "Why is Solaris 10 ZFS performance
so terrible?",
"http://mail.opensolaris.org/pipermail/zfs-discuss/2009-July/029340.html";. It
turned out that the subject was over-specific since current OpenSolaris
suffers from the same issues as proven by test results run by many
people on a wide variety of hardware.
Eventually Rich Morris posted a preliminary analysis of the performance
problem at
"http://mail.opensolaris.org/pipermail/zfs-discuss/2009-July/030169.html";
Hopefully Sun will get the prefetch algorithm and timing perfected so
that we may enjoy the full benefit of our hardware.
Thanks Bob. Can you or anyone else comment on how this bug would
interact with a zvol that's being remotely accessed? I can see clearly
how this would come into play in on a local ZFS filesystem, but how
about a remote system using the zvol through iscsi or FC?
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