ZFS performance gains real or imaginary?

[Matt Simerson]

On Dec 18, 2008, at 4:48 PM, Wes Morgan wrote:

>> On the two systems above (amd64 with 16GB of RAM and 24 1TB disks)  
>> I get about 30 days of uptime before the system hangs with a ZFS  
>> error.  They write backups to disk 24x7 and never stop. I could not  
>> anything near that level of stability with back03 (below) which was  
>> much older hardware maxed out at 4GB of RAM.  I finally resolved  
>> the stability issues on back03 by ditching ZFS and using  
>> geom_stripe across the two hardware RAID arrays.
>
> Were you doing a zfs mirror across two hardware raid arrays? The  
> performance of that type of setup would probably be sub-optimal  
> versus a zpool with two raidz volumes.

I haven't benchmarked it with -HEAD  but with FreeBSD 7, using a ZFS  
mirror across two 12-disk hardware RAID arrays (Areca 1231ML) was  
significantly (not quite double) faster than using JBOD and raidz. I  
tested a few variations (four disk pools, six disk zpools, 8 disk  
zpools, etc).

I'll be getting another 24 disk system to add to my backup pool in a  
month or two. When it arrives, I'll run some additional benchmarks  
with -HEAD and see where the numbers fall.  I'll be quite surprised if  
raidz can outrun a hardware RAID controller with 512MB of BBWC.

Matt