Pools can also be constructed using partitions rather than whole disks. Putting
<acronym>ZFS
</acronym> in a separate partition allows the same disk to have other partitions for other purposes. In particular, partitions with bootcode and file systems needed for booting can be added. This allows booting from disks that are also members of a pool. There is no performance penalty on FreeBSD when using a partition rather than a whole disk. Using partitions also allows the administrator to
<emphasis>under-provision
</emphasis> the disks, using less than the full capacity. If a future replacement disk of the same nominal size as the original actually has a slightly smaller capacity, the smaller partition will still fit, and the replacement disk can still be used.
