RAID 1 (Mirror) Volumes

You use RAID 1 devices (mirrors) to provide redundancy in storage, so the loss of a physical devices causes no interruption in data availability.

RAID 1 volumes require one or more submirrors, which must in turn be RAID 0 volumes. That is, a RAID 1 volume is constructed from RAID 0 volumes, not from raw slices or disks.