Intel SRCMR, User Manual

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26 Intel RAID Controller SRCMR User’s Guide
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 Disk Array Type
Minimum Number of
Hard Disks 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 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
Available
Capacity with
2 Hard Disks* Available
Capacity with
3 Hard Disks* Available
Capacity with
4 Hard Disks*
Available
Capacity with
5 Hard Disks*
RAID 0 2 GB 3 GB 4 GB 5 GB
RAID 1 1 GB 1 GB 1 GB 1 GB
RAID 4 NA 2 GB 3 GB 4 GB
RAID 5 NA 2 GB 3 GB 4 GB
RAID 10 NA NA 2 GB NA
*Each hard drive is assumed to have 1 GB capacity.