A hot spare pool is an ordered list (collection) of hot spares.
You can place hot spares into one or more hot spare pools to get the most flexibility and protection from the fewest slices. You could put a single slice designated for use as a hot spare into multiple hot spare pools, with each hot spare pool having different slices and characteristics. Then, you could assign a hot spare pool to any number of submirror volumes or RAID-5 volumes.
You can assign a single hot spare pool to multiple submirrors or RAID-5 volumes. However, a submirror or a RAID-5 volume can be associated with only one hot spare pool.