Compaq 3200 Reference Manual page 148

E-6 Understanding Drive Arrays
Usable Disk Space*
Disk Space Formula
(n = no. of drives)
Parity and
Data Redundancy
Minimum Number
of Drives
Comments
ll drives are the same capacity.
*A
If you require a fault-tolerant system for critical data, Compaq recommends
using RAID 5 for maximum storage space efficiency or RAID 1 if I/O
performance is more important.
If you store non-critical data, and space and performance are both important,
RAID 0 offers the best of both parameters. However, RAID 0 has no data
protection and you will have to rely on backups in the event of hardware failure.
Writer: Rickard Project: Compaq Smart Array 3200 Controller Reference Guide Comments: 340862-002
Table E-1
RAID Level Characteristics
Distributed Data Data Guarding
Guarding (RAID 5)
67% to 97% 67% to 97%
(n-1)/n
Parity distributed Dedicated parity drive
over each drive
3
Tolerant of single Tolerant of single
drive failures. Higher drive failures. Like
performance than RAID 5, RAID 4 uses
RAID 4. Uses the the least amount of
least amount of storage capacity for
storage capacity for fault tolerance.
fault tolerance.
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Mirroring
(RAID 4) (RAID 1)
50%
(n-1)/n n/2
Duplicate data
3 2
Tolerant of multiple,
simultaneous drive
failures. Higher
performance than
RAID 4 or 5. RAID 1
uses the most
storage capacity for
fault tolerance, and
requires an even
number of drives.
No Fault Tolerance
(RAID 0)
100%
n
None
1
Best performance,
but data is lost if any
drive in the logical
drive fails. RAID 0
uses no storage
space for fault
tolerance.