8.0-RELEASE/amd64 - full ZFS install - low read and write disk performance

Bob Friesenhahn bfriesen at simple.dallas.tx.us
Mon Jan 25 05:55:06 UTC 2010

On Mon, 25 Jan 2010, Dan Naumov wrote:
> I've checked with the manufacturer and it seems that the Sil3124 in
> this NAS is indeed a PCI card. More info on the card in question is
> available at http://green-pcs.co.uk/2009/01/28/tranquil-bbs2-those-pci-cards/
> I have the card described later on the page, the one with 4 SATA ports
> and no eSATA. Alright, so it being PCI is probably a bottleneck in
> some ways, but that still doesn't explain the performance THAT bad,
> considering that same hardware, same disks, same disk controller push
> over 65mb/s in both reads and writes in Win2008. And agian, I am
> pretty sure that I've had "close to expected" results when I was

The slow PCI bus and this card look like the bottleneck to me. 
Remember that your Win2008 tests were with just one disk, your zfs 
performance with just one disk was similar to Win2008, and your zfs 
performance with a mirror was just under 1/2 that.

I don't think that your performance results are necessarily out of 
line for the hardware you are using.

On an old Sun SPARC workstation with retrofitted 15K RPM drives on 
Ultra-160 SCSI channel, I see a zfs mirror write performance of 
67,317KB/second and a read performance of 124,347KB/second.  The 
drives themselves are capable of 100MB/second range performance. 
Similar to yourself, I see 1/2 the write performance due to bandwidth 

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

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