You may already know what is ZFS. Maybe you don’t know what is SMR, or Shingled Magnetic Recording.
Long story short: a drive which performs SMR as writing system overlaps tracks between them for increase the space available on the magnetic drive. For writing it in the correct way, the data is stored into a cache, then written when the drive is ready to take care of that.
Yes, it slows the writing speed. A lot.
Compared to CMR (conventional magnetic recording) or PMR (perpendicular magnetic recording) the peak latency is increased from 0.1 sec to 1.3 secs!. If you can hear something distant, it’s the echo of my jaw hitting the floor.
Putting into another example (took from LTT video, coming from a IT specialist
the rebuild of a 1 4TB disk out of 8 disks ZFS array tooks 16 hours with CMR/PMR, it took 9.5 *days with an SMR drive. Not just Bad, but Hyper-cube-bad-squared. And cube at the end.
Synology took the occasion for say “hey WD, your Red drives with SMR are not good for us”.
I can understand why (seems that maybe even other FS do not like so much DM-SMR drives)
Some more links…
Buy smart your next drive, buddies… And be prepared: class action is coming.