User guide

D-6 Compaq Smart Array 431 Controller User Guide
Table D-1
RAID Level Characteristics
Distributed Data
Guarding (RAID 5)
Mirroring
(RAID 1)
No Fault tolerance
(RAID 0)
Striping and Mirroring
0+1
Usable Disk Space*
67% to 93 % 50% 100% 50%
Disk Space Formula
(n = no. of drives)
where: n is the
number of drives in
the array (up to 15)
(n-1)/n n/2 n n/2
Parity and
Data Redundancy
Parity distributed
over each drive
Duplicate data None Duplicate data
Minimum Number
of Drives
321 4
Comments
Tolerant of single
drive failures. Uses
the least amount of
storage capacity for
fault tolerance.
Tolerant of multiple,
simultaneous drive
failures.** Higher
performance than
RAID 5. Uses the
most storage
capacity for fault
tolerance. Requires
an even number of
drives.
Best performance,
but data is lost if any
drive in the logical
drive fails. Uses no
storage space for
fault tolerance.
Tolerant of multiple,
simultaneous drive
failures.** Higher
performance than
RAID 5. Uses the most
storage capacity for
fault tolerance.
Requires an even
number of drives
* All drives are the same capacity ** As long as failed drives are not mirrored to each other. (Can lose one array per mirrored
pair.)
If you require a fault-tolerant system for critical data, use RAID 5 for
maximum storage space efficiency or RAID 1 if maximum performance and
redundancy are critical.
If you will be storing non-critical data and space and performance are both
important, RAID 0 offers the best of both parameters.
CAUTION: RAID 0 has no data protection and you must rely on backups in case
of hardware failure.