Each level of RAID spreads the data across the drives of the array in a different way and is optimized for specific situations. For our purposes, we are going to concentrate on the most common RAID levels used today.

This RAID level combines two or more hard drives in a way that the data (ABCD...in the yellow pots) coming from the user is cut into manageable blocks. These blocks are striped across the different drives of the RAID 0 array. By doing this, two or more hard drives are combined and the read/write performance, especially for sequential access, can be improved. However, no redundancy information is stored in a RAID 0 array, which means that if one hard drive fails, all data is lost. This lack of redundancy is also stated in the number 0, which indicates no redundancy. RAID 0 is thus usually not used in servers where security is a concern.

Advantage:

Highest transfer rates

Disadvantage:

No redundancy, i.e. if one disk fails all data will be lost

Application:

Typically used in workstations for temporary data and high I/O rate

In a RAID 1 system, identical data is stored on two hard disks (100 percent redundancy). When one disk drive fails, all data is immediately available on the other without any impact on the performance or data integrity. We refer to "Disk Mirroring" when two disk drives are mirrored on one SCSI channel. If each disk drive is connected to a separate SCSI channel, we refer to this as "Disk Duplexing" (additional security). RAID 1 represents an easy and highly efficient solution for data security and system availability.

Advantage:

High availability, one disk may fail, but the Logical Drive with the data is still available

Disadvantage:

Requires 2 disks but only uses storage of one

Application:

Typically used for smaller systems where capacity of 1 disk is sufficient and for boot disks

Unlike RAID 4, the parity data in a RAID 5 disk array are striped across all disk drives. The RAID 5 disk array delivers a more balanced throughput. Even with small data blocks, which are very common in multitasking and multi-user environments, the response time is very good. RAID 5 offers the same level of security as in RAID 4: when one disk drive fails, all data is still fully available. The missing data is recalculated from the data that remains available and from the parity information.

Advantage:

High availability, one disk may fail, but the Logical Drive with the data is still available

Advantage:

Has a very good use of disk capacity (array of n disks, n-1 is used for data storage)

Disadvantage:

Has to calculate redundancy information, which limits write performance

Application:

Typically used for larger systems for data storage due to efficient ratio of installed capacity to actual available capacity