User`s manual

Appendices
C.4. RAID 1
RAID 1 implements disk mirroring where a copy of the same data is
recorded onto two sets of striped drives. By keeping two copies of data on
separate disks or arrays, data is protected against a disk failure. If a disk on
either side fails at any time, the good disks can provide all of the data
needed, thus preventing downtime.
In disk mirroring, the total disk capacity is equivalent to half the sum of the
capacities of all drives in the combination. For example, combining four
1GB drives would create a single logical drive with a total disk capacity of
2GB. This combination of drives appears to the system as a single logical
drive.
RAID 1 is simple and easy to implement; however, it is more expensive as it
doubles the investment required for a non-redundant disk array
implementation.
Figure C-3: RAID1 Storage
In addition to the data protection RAID 1 provides, this RAID level also
improves performance. In cases where multiple concurrent I/Os are
occurring, these I/Os can be distributed between two disk copies, thus
reducing total effective data access time.
C.5. RAID 1(0+1)
RAID 1(0+1) combines RAID 0 and RAID 1 – mirroring and disk striping.
RAID (0+1) allows multiple drive failure because of the full redundancy of
the hard disk drives. If more than two hard disk drives are chosen for RAID
1, RAID (0+1) will be performed automatically.
RAID Levels App-15