HP Compaq Integrated Smart Array Controller User Manual

Page 112

B-6 Compaq Integrated Smart Array Controller User Guide

Compaq Confidential – Need to Know Required

Writer: CDresden Project: Compaq Integrated Smart Array Controller User Guide Comments:

Part Number: 153236-001 File Name: i-appb Understanding Drive Arrays.doc Last Saved On: 8/27/99 11:35 AM

The fault-tolerance method you choose affects the amount of available disk
storage capacity and the performance of your drive array. The following table
lists all supported RAID levels for Integrated Smart Array Controller, and it
illustrates how the fault-tolerance method you select affects performance and
capacity.

Table B-1

RAID Level Characteristics

Distributed Data
Guarding (RAID 5)

Mirroring
(RAID 1)

No Fault Tolerance
(RAID 0)

Striping and Mirroring
(RAID 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

Parity and
Data Redundancy

Parity distributed
over each drive

Duplicate data

None

Duplicate data

Minimum Number
of Drives

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 have the same capacity ** As long as failed drives are not mirrored to each other.

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 are storing noncritical data, and both space and performance are both
important, RAID 0 provides the best option.