For hot spares as temporary fixes - Hot spares are not designed to remain a permanent part of your configuration. They need to be replaced with repaired or new slices.
For hot spares and state database replicas - Hot spares cannot contain state database replicas.
For cross-controller assigning - Ideally, slices added to the hot spare pool should be attached to different controllers. This ensures availability of data due to controller error or failure.
For wrong-size hot spares - Do not associate hot spares of the wrong size with submirrors or RAID5 metadevices.
For hot spares marked In Use - Make sure that all hot spares within a hot spare pool are not marked In-Use.
For one-way mirrors and hot spares - Do not assign a hot spare pool to a submirror in a one-way mirror.
Hot spares are used on a first-fit basis - When adding hot spares of different sizes to a hot spare pool, add the smaller slices first.