Intel SRCU32 - RAID Controller, User Manual

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26 Intel RAID Controller SRCU32 User’s Guide
Table 1. Hard Drive SCSI Parameters (continued)
Parameter Setting/Value Description
Tagged Queues Not
Configurable
When enabled, this feature allows the SCSI hard drive to execute more
than one command at a time.
Disk Read and
Write Cache On / Off For performance reasons, the Read Ahead and Write cache of the hard
drives should always be on.
Domain
Validation Not
Configurable
Using the <F4> key while in this menu accesses this parameter. When
Domain Validation is set to
On , Domain validation allows for a cyclical
check of the correct data transfer at a given rate.
Choosing a Configuration
How Many Hard Drives Should Be Integrated Into the Disk Array?
The number of physical drives the Intel RAID Controller SRCU32 can run determines the
maximum number of physical drives in a disk array. The minimum number of hard drives required
for any array depends of the RAID level you wish to realize. The desired usable disk space of the
disk array as well as the issues discussed in the following sections (What Level of Redundancy is
Needed and Are Hot Fix Drives Needed) have a direct impact on the number of physical hard
drives needed for an array.
Table 2. RAID Level, Array Type, and Hard Drive Requirements
RAID Level
Disk Array Type Minimum Number of
Hard Drives Required
RAID 0 Data Striping 2
RAID 1 Disk Mirroring 2
RAID 4 Data Striping with Parity Drive 3
RAID 5 Data Striping with Striped Parity 3
RAID 10 Data Striping and Mirroring 4
What Level of Redundancy is Needed?
RAID 0 (data striping) provides no redundancy but has high data throughput. With RAID 1
(disk mirroring) the data is 100% redundant because it is mirrored on other SCSI hard drives.
RAID 1 provides the highest level of redundancy, but is also the most expensive solution. A
combination of RAID levels 0 and 1 is RAID 10. Two RAID 0 stripe sets are mirrored. If one
drive fails, the data is available on the mirrored drive.
With RAID 4 (data striping with a dedicated parity drive) and RAID 5 (data striping with parity
striped across all RAID disks), parity information is calculated from the data with a simple
mathematical operation (eXclusive OR, XOR), and stored either on one dedicated drive (RAID 4)
or to all drives (RAID 5). Should one drive fail, the data of the defective drive can be reconstructed
using the remaining user data and the previously calculated parity data. RAID levels 4, 5 and 10
can tolerate the failure of one drive just as RAID 1, however RAID 4, RAID 5, or RAID 10 are less
expensive because of their efficient ratio of available to installed capacity.