When To (and not to) use RAID-Z

RAID-Z is the technology used by ZFS to implement a data-protection scheme which is less costly than mirroring in terms of block overhead. Here, I’d like to go over, from a theoretical standpoint, the performance implication of using RAID-Z. The goal of this technology is to allow a storage subsystem to be able to deliver the stored data in the face of one or more disk failures. This is accomplished by joining multiple disks into a N-way RAID-Z group. Multiple RAID-Z groups can be dynamically striped to form a larger storage pool.