Compaq Smart Array 221 User Manual page 108

C-6 Understanding Drive Arrays
Guarding (RAID 5)
Usable Disk Space*
Disk Space Formula
(n = no. of drives)
where: n is the
number of drives in
the array (up to 15)
Parity and
Data Redundancy
Minimum Number
of Drives
Tolerant of single
Comments
drive failures. Uses
the least amount of
storage capacity for
fault tolerance.
*All drives are the same capacity
If you require a fault tolerant system for critical data, Compaq recommends
using 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.
Writer: Karen Hale Project: Compaq Smart Array 221 Controller User Guide Comments: 388541-001
Table C-1
RAID Level Characteristics
Distributed Data Mirroring
(RAID 1)
67% to 93 %
(n-1)/n
Parity distributed Duplicate data
over each drive
3
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.
** As long as failed drives are not mirrored to each other. (Can lose one array per mirrored pair.)
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No Fault Tolerance
(RAID 0)
50% 100%
n/2 n
None
2 1
Best performance,
but data is lost if any
drive in the logical
drive fails. Uses no
storage space for
fault tolerance.
Striping and Mirroring
0+1
50%
n/2
Duplicate data
4
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