WHEN TO (AND NOT TO) USE RAID-Z

WHEN TO (AND NOT TO) USE RAID-Z: "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. To store file data onto a RAID-Z group, ZFS will spread a filesystem (FS) block onto the N devices that make up the group. So for each FS block, (N - 1) devices will hold file data and 1 device will hold parity information. This information would eventually be used to reconstruct (or resilver) data in the face of any device failure. We thus have 1 / N of the available disk blocks that are used to store the parity information. A 10-disk RAID-Z group has 9/10th of the blocks "