Well zfs will use all the ram it has available for caching. You really dont need a hba unless you want bleeding edge io but you would be surprised at how fast an intel ich10 can be and works perfect with 99% of set ups. However you only have 6 ports on an ich10 controller.
I would go with an ecc supporting amd 965 quadcore and m1015 for the best performance per dollar or an intel i3-3000 series dual core with ich10 and 6 disc for another highly cost effective rig. I just shelled out $2000 for my e5-1620 piweres 32g zfs box.
Per my research ECC RAM is crucial for ZFS, or you are risking your data.
ZFS does eat lots of RAM if available as @ tangoseal points out. Smaller RAM will work but will reduce performance. ZFS eats CPU as well, especially if compression is turned on, even only LZJB. per my current experience over the several days, if another VM on the same ESXi host reads files for the full speed the host CPU can go to 100%. the Solaris VM is given 6 vCPU and the other VM is using 8 reading threads with 4 vCPU.
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