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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