dRAID

dRAID is a variant of raidz that provides integrated distributed hot spares which allows for 
faster resilvering while retaining the benefits of raidz. A dRAID vdev is constructed from multiple 
internal raidz groups, each with D data devices and P parity devices. These groups are distributed 
over all of the children in order to fully utilize the available disk performance. This is known as 
parity declustering and it has been an active area of research. The image below is simplified, but 
it helps illustrate this key difference between dRAID and raidz.

dRAID Introduction

Create DRAID with 1 parity and 2 redundancy (on 3 disks):

zpool create backup draid1:2d <disk1> <disk2> <disk3>

draid2:2d:14c:1s
     |  |  |  |
     |  |  |  L-> one spare
     |  |  |
     |  |  L-> total number of disks to use
     |  |
     |  L-> number of data disks per disk group
     |
     L-> number of parity disks per disk group