ZFS I/O Throughput question..

[Pawel Jakub Dawidek]

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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