I'm building a simple storage server for home usage, and I'm modelling it slightly after our Solaris storage servers at work. But at a smaller scale. The basic layout will be a chassis with four hot swap disk slots, Solaris on an SSD or an USB stick, and two 1 TB disks in a mirror set. This will leave me two empty hotswap slots to add more storage when needed.
At work I wouldn't consider a two disk mirror without a hotspare, given the risk that the second disk will be from the same factory batch as the first and might fail with identical symtoms ten minutes after the first disk fails. At home I don't feel like paying for hotspares or more disks, but would like some protection against this.
What's the consensus on mixing drives in a mirror set, say one WD RE4 and one Seagate Constellation ES? It should at least minimize the possibility of a systematic manufacturing defect taking out both disks. A small size difference is no problem for ZFS to handle, but are there any other potential pitfalls or horror stories here?