ZFS and CPU usage

[trumee]

I have a Supermicro C3558 motherboard which is 4 threads @2.2GHz. The system has a two consumer SSD's. I installed Pfsense on one of the SSDs and the load average was "0.81, 0.69, 0.54" with CPU hovering about 11%.

I wiped this setup and reinstalled the same config on ZFS with mirrored SSDs. The load average moved upto "1.04, 0.96,0.92" with CPU hovering around 20%.

ZFS is using double to CPU with the same configuration. Is this expected?

Packages I have installed are SNORT, PfblockerNG and Status_Traffic_Totals.

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I also did a test without any packages, with ZFS load average was "0.65, 0.62, 0.52" and CPU was about 11%. Disk bandwidth is like,

zpool iostat 5
               capacity     operations    bandwidth
pool        alloc   free   read  write   read  write
----------  -----  -----  -----  -----  -----  -----
zroot        511M   117G      0     41  23.3K   193K
zroot        511M   117G      0     38      0   174K
zroot        511M   117G      0     38      0   173K
zroot        511M   117G      0     41      0   190K
zroot        511M   117G      0     39      0   176K
zroot        511M   117G      0     39      0   180K
zroot        511M   117G      0     39      0   178K
zroot        511M   117G      0     40      0   182K
zroot        511M   117G      0     38      0   175K
zroot        511M   117G      0     39      0   179K
zroot        511M   117G      0     50      0   220K
zroot        511M   117G      0     39      0   180K