@ Tekkie
Save yourself a little time, it's easier to change the settings than making a CD and waiting for MemTest. @Buhmi seemed reluctant to try what I suggested and it helped him. Just because you have 8GB of RAM doesn't mean it's allocated correctly for ZFS. You probably want to allocate, or at least set the max so it uses as much of your 8GB as possible, with the exception of leaving enough for regular applications/OS or plug-ins to run. I'm not an expert on ZFS tuning, but I have done a little reading. I may not be able to spout of details, but it's a quick change and its a lot faster to try. If it doesn't help give the MemTest a try. I'll look up some look into what those values should be for 8GB and update this post.
UPDATE:
Ok, there are a lot of different opinions on recommended values based on your RAM. If you search google for "vm.kmem_size recommended for 8GB", you can read them yourself, and then there are other settings that should also be adjusted based on what you set you VM.KMEM values at. So for you I would try vm.kmem_size="4096" and for vm.kmem_size_max="6144M". You should also consider adjusting vfs.zfs.arc_min & vfs.zfs.arc_max, but please, I'm not an expert do a little reading. The settings I suggested are just a starting point, but I'll bet you stop seeing your problems.
OH, don't forget to reboot after you make changes!
Having the vm.kmem_size_max at 6GB will leave 2GB for other apps and the OS *IF* ZFS does happen to use that much. I think ZFS will use all the RAM you can give it, especially when you add encryption, compression, deduplication etc. etc. later on.
@joe
You just forced me to open up my case and use my IR temp sensor to find out the answer ;-) It's 100 degrees F.... The disks are another story since they're stacked horizontally (bad case design) the bottom disk is 88 and the top disk is 94. I wanted to mod the drive cage so the drive are oriented vertically/sideways so the temp doesn't accumulate on the top disk, but haven't had time so far.