After 2 months of attempts, we have successfully upgraded to 4.4(hardened) and the latest ZFS development branch. The latest ZFS development branch contains a new feature called ABD which is meant to reduce memory waste by changing from the standard slab allocator for cache objects to a scatter list. Initial testing on other machines showed nice improvements. Attempted to upgrade to 4.8(hardened) at the same time, which ran into some roadblocks with boot-time kernel panics. Will try upgrading to a newer kernel in the future.