3 ms·
That makes sense. Usually the received wisdom I hear is "RAIDZ is slower due to the parity calculations", which has always seemed dubious to me on modern CPUs,
by didntcheck 3y ago
That makes sense. Usually the received wisdom I hear is "RAIDZ is slower due to the parity calculations", which has always seemed dubious to me on modern CPUs, given we can do much more complex compression and encryption at way faster then disk speed (for HDDs, at least)
- someplaceguy 3y agoUsually what makes RAID-Z slower is not really the parity calculations, it's the fact that each RAID-Z vdev only has the read IOPS of the slowest disk in it. So for example, a pool with 2 RAID-Z vdevs each containing 5 disks effectively has only 2x the IOPS of a single disk, while a pool with 5 mirror vdevs (i.e. RAID-10) has 10x the IOPS of a single disk. It's not a big problem if you mostly do sequential I/O but it's a huge difference if/when you do small random reads (e.g. traversing a non-cached directory tree). In the context of resilvers, currently RAID-Z pools can only be done by traversing the block tree which, due to fragmentation of CoW filesystems, usually leads to a lot of random reads/writes, while a RAID-10 pool can basically resilver a pool while doing almost fully sequential I/O which can be much, much faster.