To clarify, you're redistributing the missing data across all of the other disks in the array simultaneously, rather than to one disk sequentially. Let's say y

To clarify, you're redistributing the missing data across all of the other disks in the array simultaneously, rather than to one disk sequentially. Let's say you've got an array with 10 disks and 100TB of data. You experience a single-disk failure. If you're running a RaidZ, you have to write the lost data (100TB / 10 disks) to the single replacement disk. Writing 10TB of data to a single disk takes quite a while, especially on inexpensive SATA disks. If you were running a dRAID with equivalent redundancy settings, you have to write (100 / 10)TB to the 9 remaining disks in the array. Each disk will have to write about 1.2 TB of data in parallel. Writing 1.2TB to each disk should be roughly ~5-10x faster than writing 10TB sequentially.