RAID Types
RAID - a data storage created by combining several disks to a single storage, usually with large capacity.
Hardware and software RAID
There are two ways to create an array:
- based on software (called a software RAID),
- based on a standalone controller (called a hardware RAID).
Many of the operating systems have a built-in capability to create RAID.
However, you should keep in mind that software RAID0 and RAID5 cannot contain a boot partition.
Storing data on RAID
There are the following methods to write data to RAID.
-
Mirroring: It is required to use no less than two disks.
The same data is written on two of the array member disks.
The example of such an array is RAID 1 (sometimes called Mirror).
-
Striping: It is required to use no less than two disks.
The data blocks are written on each of the array member disks in turn.
The example of such an array is RAID 0.
-
Parity: It is required to use no less than three disks.
Along with data blocks, some checksum (called parity) is written to provide array redundancy.
The examples are RAID 5 and RAID 6.
RAID levels
RAID 0.
The array is based on the striping technique.
You need no less than two disks to create RAID 0.
Such an array isn't a fault-tolerant RAID, but it provides better performance than a single disk.
It is a cheap RAID type because all disk space is used with no overhead.
RAID 1.
The array is based on the mirroring technique.
You need two disks to create RAID 1.
It is pretty expensive choice because 100% disk space overhead is required.
RAID 5 and RAID 6.
The array is based on the parity and striping techniques.
You need no less than three disks to create RAID 5.
This array provides a single-disk fault tolerance by implementing a parity function.
It doesn't give significant performance advantages on writes.
RAID 6 uses two different parity functions and can thus withstand a double hard drive failure.
RAID 10.
The array is based on the mirroring and striping techniques.
It provides a single-drive redundancy.
This array is an expensive type of RAID because of significant disk space overhead.
|