Choosing A Configuration; How Many Hard Disks Should Be Integrated Into The Disk Array; What Level Of Redundancy Is Needed; Raid Level, Array Type, And Hard Disk Requirements - Intel SRCMR - RAID Controller User Manual

Choosing a Configuration

How many Hard Disks should be Integrated into the Disk Array?

The maximum number of physical drives in a disk array is determined by the number of physical
drives the Intel RAID Controller SRCMR can run. The minimum number of hard disks 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 disks
needed for an array.
Table 2.

RAID Level, Array Type, and Hard Disk Requirements

RAID Level
RAID 0
RAID 1
RAID 4
RAID 5
RAID 10

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 disks. 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.
Table 3.

RAID Level, Hard Drives, and Usable Storage Capacity

RAID Level
RAID 0
RAID 1
RAID 4
RAID 5
RAID 10
*Each hard drive is assumed to have 1 GB capacity.
26
Disk Array Type
Data Striping
Disk Mirroring
Data Striping with Parity Drive
Data Striping with Striped Parity
Data Striping and Mirroring
Available Available
Capacity with Capacity with
2 Hard Disks* 3 Hard Disks*
2 GB 3 GB
1 GB 1 GB
NA 2 GB
NA 2 GB
NA NA
Minimum Number of
Hard Disks Required
2
2
3
3
4
Available Available
Capacity with Capacity with
4 Hard Disks* 5 Hard Disks*
4 GB 5 GB
1 GB 1 GB
3 GB 4 GB
3 GB 4 GB
2 GB NA
Intel RAID Controller SRCMR User's Guide