Let's say I have a ZFS pool with a fast SSD and I want to add a magnetic hot spare.

Will the pool slow down to the hot spare's speed?

2 Answers 2


Yep, totally.

It's not worth having dissimilar disks in the same data pool. I wouldn't even mix and match SATA and SAS disks as data drives in a single pool. You should stick with a like-model SSD if you want to have a hot-spare. I'd recommend using it as a cold-spare, assuming hot-pluggable disks, though.

  • A spare by definition isn't accessed during normal operation, so how could the speed of the spare possibly have any influence of the performance of the pool?
    – kasperd
    Oct 31, 2015 at 19:06
  • Because it wouldn't make sense if it came into use. I wasn't giving a direct answer to the question because the premise was wrong.
    – ewwhite
    Oct 31, 2015 at 19:14

No, unless it gets used. You can try this and everything is fast and smooth until a drive breaks in the main pool, then you're back to slow land (resilver can be snappy though, if you can avoid fragmentation).

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