RAID 0 is the fastest RAID mode and requires at least two drives. RAID 0 combines all the available capacities of each disk to create one logical volume to mount to a computer. If one physical disk in the array fails, the data on all the disks becomes inaccessible because parts of the data have been written to all the disks. RAID 0 effectively distributes the workload of writing or reading data equally between all disks which make up the array.
RAID 1 is a 2 disk configuration only. This RAID mode provides safety since all data is written to both drives at the same time. In the event of a single drive failure, data remains available on the other drive. Performance can be slightly reduced compared to using a single drive, however the difference is typical negligible. RAID 1 is a good choice when safety is more important than speed, however it is extremely important to keep in mind that a RAID 1 DOES NOT COUNT AS A BACKUP. In the end, the RAID is treated as a single volume and any file corruption will be duplicated on both drives. Also, if the hardware managing the RAID experiences any issues, this can lead to corruption of the volume.
RAID 5 combines the striping of RAID 0 with data redundancy in an array with a minimum of three disks. In a 3 disk example, data is split across 2 drives and the 3rd is used for parity. In a 5 disk example, data is split across 4 drives and the 5th is used for parity. If one physical disk fails, the data from the failed disk can be rebuilt onto a replacement disk. No data is lost in the case of a single drive failure, but if a second disk fails before data can be rebuilt to a replacement drive, all data in the array will be lost.
RAID 10 is also known as RAID 1+0 and combines the attributes of RAID 1 and RAID 0. It is a “mirror of stripes”, meaning that data is striped across two mirrored arrays. The striping occurs between arrays and the mirroring occurs within the same array. In a RAID 10 array, one disk from each mirrored pair can fail without data loss. However, the working disk in an array with a failed disk becomes a weak point for the entire array. If the second disk in a mirrored pair fails, the entire array is lost.
JBOD is not technically a RAID mode, since all disks are independent, with no collective properties. Each physical disk is mapped to a different logical volume. As a result, one volume for each disk will mount on the computer. No protection is provided, so if a disk fails, all data contained on that disk is lost.
Note: RAID (in most forms) is meant to keep workflow from halting in case of a drive failure. There is no RAID mode that can act as a proper backup for the following reasons:
- RAIDs are treated as single volumes; if data becomes corrupted, any copies of the data created within the RAID array will also be corrupted.
- RAIDs are heavily dependent on the hardware managing them. If this hardware experiences technical issues, this can result in the RAID itself becoming corrupted and any data stored on it.
- RAIDs do not protect data from physical calamities such as fires, floods, theft or other.
