What is raid technology used for?

Answer 1

As a rule, the most common RAID levels in use today are:

• No RAID - logical data volumes exist within single physical drive
• RAID 0 - logical data volumes striped across multiple physical drives with no parity/data protection. Common, but not necessarily a good idea (backup is important here).
• RAID 1 - logical data volumes mirrored, bit-for-bit, between two physical drives (in come implementations, additional mirror drives can be created)
• RAID 5 - logical data volumes striped across multiple drives with parity/data protection generated and distributed among all drives in the RAID set.

Three notes come to mind:

1. Depending on implementation, RAID devices appear as a logical (or physical) drive to the OS or application. Software RAID, configurable in utilities such as in Windows Disk Manager or MDADM (Linux) works just below the operating system, providing a representation of a virtual physical disk to the operating system.
2. Sometimes, RAID levels are combined, such as RAID 0+1 (striped, then mirrored) or RAID 1+0/10 (mirrored, then striped).
3. As drives and RAID sets get larger (2-3 TB+), the time to recalculate/recover data for a failed physical drive becomes prohibitive, both in downtime/degraded operation and vulnerability to data loss from an additional failure.

A number of new technologies, as well modifications to classic RAID, are being explored to address shortcoming 3.

Answer 2

RAID is a method of combining several hard disk drives into one logical unit (two or more disks grouped together to appear as a single device to the host system).