RAID mirrors to speed backups: A RAID set with two mirrors can be
used to make backups faster. Initially, the system has identical data on
three sets of disks, known as a triple-mirror configuration. When it is
time to do backups, one mirror set is broken off, again in coordination
with database systems and the OS to make sure that the data mirror
is in a consistent state. Now the backup can be done on the mirror
that has been separated. Done this way, backups will not slow down
the system. When the backup is complete, the mirror is reattached, the
rebuild happens, and the system is soon back to its normal state. The
rebuild does not affect performance of the production system as much,
because the read requests can be distributed between the two primary
mirrors.