HP ProLiant 800 SMART-2DH Array Controller Reference Guide - Page 139

Table D-1, RAID Level Characteristics, No Fault Tolerance

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D-6 Understanding Drive Arrays Table D-1 RAID Level Characteristics Distributed Data Guarding (RAID 5) Data Guarding (RAID 4) Mirroring (RAID 1) No Fault Tolerance (RAID 0) Usable Disk Space* 67% to 93% 67% to 93% 50% 100% Disk Space Formula (n-1)/n (n-1)/n n/2 n (n = no. of drives) Parity and Parity distributed Dedicated parity drive Duplicate data None Data Redundancy over each drive Minimum Number 3 3 2 1 of Drives Comments Tolerant of single drive failures. Higher performance than RAID 4. Uses the least amount of storage capacity for fault tolerance. Tolerant of single drive failures. Like RAID 5, uses the least amount of storage capacity for fault tolerance. Tolerant of multiple, simultaneous drive failures. Higher performance than RAID 4 or 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. * 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 I/O performance is more important. If you will be storing 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 case of hardware failure. Writer: Pamela King Project: SMART-2DH Array Controller Reference Guide Comments: 295469-002 File Name: K-APPD.DOC Last Saved On: 2/27/98 12:06 PM COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED

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D-6
Understanding Drive Arrays
Writer: Pamela King
Project: SMART-2DH Array Controller Reference Guide
Comments: 295469-002
File Name: K-APPD.DOC
Last Saved On: 2/27/98 12:06 PM
COMPAQ CONFIDENTIAL - NEED TO KNOW REQUIRED
Table D-1
RAID Level Characteristics
Distributed Data
Guarding (RAID 5)
Data Guarding
(RAID 4)
Mirroring
(RAID 1)
No Fault Tolerance
(RAID 0)
Usable Disk Space*
67% to 93%
67% to 93%
50%
100%
Disk Space Formula
(n = no. of drives)
(n-1)/n
(n-1)/n
n/2
n
Parity and
Data Redundancy
Parity distributed
over each drive
Dedicated parity drive
Duplicate data
None
Minimum Number
of Drives
3
3
2
1
Comments
Tolerant of single
drive failures. Higher
performance than
RAID 4. Uses the
least amount of
storage capacity for
fault tolerance.
Tolerant of single
drive failures. Like
RAID 5, uses the least
amount of storage
capacity for fault
tolerance.
Tolerant of multiple,
simultaneous drive
failures. Higher
performance than
RAID 4 or 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.
*
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 I/O performance is more important.
If you will be storing 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 case of hardware failure.