Raid 1 Mirrored Pair - EMC CX700 Planning Manual

RAID 1 Mirrored Pair

larger. By using both the read and write cache, a RAID 3 group can
handle several concurrent streams of access.
RAID 3 Groups do not require any special buffer area. No fixed
memory is required to use write cache with RAID 3. Simply allocate
write cache as you would for RAID 5, and ensure that caching is
turned on for the LUNs in the RAID 3 Groups. Access to RAID 3
LUNs is compatible with concurrent access to LUNS of other RAID
types on the storage system.
A RAID 1 Group consists of two disks that are mirrored
automatically by the storage-system hardware. With a RAID 1 Group,
you can create multiple RAID 1 LUNs to apportion disk space to
different users, servers, and applications.
RAID 1 hardware mirroring within the storage system is not the same
as software mirroring, remote mirroring, or hardware mirroring for
other kinds of disks. Functionally, the difference is that you cannot
manually stop mirroring on a RAID 1 mirrored pair, and then access
one of the images independently. If you want to use one of the disks
in such a mirror separately, you must unbind the mirror (losing all
data on it), rebind the disk as the type you want, and software format
the newly bound LUN.
With a storage system, RAID 1 hardware mirroring has the following
advantages:
automatic operation (you do not have to issue commands to
initiate it)
physical duplication of images
a rebuild period that you can select during which the SP recreates
the second image after a failure
RAID Types and Trade-offs
2-7
RAID Types