RAID 1 (Mirrors) Overview

A RAID 1 volume, or mirror, is a volume that can copy the data in RAID 0 volumes (stripes or concatenations), or generically called submirrors, to other volumes. This process is called mirroring data. (Mirroring is also known as RAID level 1.)

A RAID 1 volume provides redundant copies of your data. These copies should be located on separate physical devices to guard against device failures.

RAID 1 volumes require an investment in disks. You need at least twice as much disk space as the amount of data you have to mirror. Because storage management software must write to all submirrors, RAID 1 volumes can also increase the amount of time it takes for write requests to be written to disk.

After you configure a RAID 1 volume, it can be used just as if it were a physical slice.

You can also use a RAID 1 volume for online backups. Because the submirrors contain identical copies of data, you can take a submirror offline and back up the data to another medium - all without stopping normal activity on the RAID 1 volume. You might want to do online backups with a three-way mirror so that the RAID 1 volume continues to copy data to two submirrors. Also, when the submirror is brought back online, it will take a while for it to sync its data with the other two submirrors.

You can create RAID 1 volumes for any file system, including existing file systems. You can also use a RAID 1 volume for any application, such as a database. You can create a one-way mirror and attach another submirror to it later.