A pool is similar to a volume group, with the following differences.
The data in a pool is stored randomly on all drives in the pool, unlike data in a volume group, which is stored on the same set of drives.
A pool has less performance degradation when a drive fails, and takes less time to reconstruct.
A pool has built-in preservation capacity; therefore, it does not require dedicated hot spare drives.
A pool allows a large number of drives to be grouped.
A pool does not need a specified RAID level.