ZFS I/O Throughput question..
Christopher Watson
bsdunix44 at gmail.com
Fri Sep 17 20:09:56 UTC 2010
I'll be able to test that in 8 hours. Thanks for the reply! I'll post results then. Also, what *is* the recommended way to get a more accurate test of file I/O regarding zfs? dd clearly isn't the best tool. Postmark? Blogbench?
Chris
Sent from my iPhone
On Sep 17, 2010, at 2:35 PM, Pawel Jakub Dawidek <pjd at FreeBSD.org> wrote:
> On Wed, Sep 15, 2010 at 03:05:46AM -0500, Chris Watson wrote:
>> I have been testing ZFS on a home box now for a few days and I have a
>> question that is perplexing me. Everything I have read on ZFS says in
>> almost every case mirroring is faster than raidz. So I initially setup
>> a 2x2 Raid 10 striped mirror. Like so:
> [...]
>
> Could you try running something like this:
>
> # apply "dd if=/dev/ada%1 of=/dev/null bs=1m count=5000 &" 2 3 4 5
>
> This will tell us how much of total throughput do you have.
> If you can destroy your data, you may also try this:
>
> # apply "dd if=/dev/null of=/dev/ada%1 bs=1m count=5000 &" 2 3 4 5
>
> If you disks cannot work at full speed in parallel this might explain
> what you're seeing. Mirror send to disk twice as much data as it
> receives and RAIDZ sends only 33% more data in four disk case.
>
> And no, there are neither special RAIDZ optimizations not special mirror
> pesimizations in FreeBSD.
>
> --
> Pawel Jakub Dawidek http://www.wheelsystems.com
> pjd at FreeBSD.org http://www.FreeBSD.org
> FreeBSD committer Am I Evil? Yes, I Am!
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