Glossary
RAID
Redundant Array of Independant Disks
The combination of several hard drives, to get data security. Also used later to increase data throughput. Meanwhile all combinations of media is commonly called RAID.
Overview over the most importand RAID levels:
RAID 0 (Striping): Data is being written devided on two or more hard drives. This RAID level produces a high data thoughput, because one hard drive can read (or write) data, while the other is positioning it's head. The hard drives must have the same capacity.
RAID 1 (Mirroring): Data is being written simultanously on two or more drives. The contents of all hard drives are identical. If a drive crashes, the computer can still work with the other hard drive(s). After changing the defect drive, the controller copies the data from the spare HDD to the new one, so that the contents are equal again.
RAID 4: This RAID level requires at least three HDDs. The first two are used for normal data, the third one is used for parity data. If a hard drive fails, the controller is able to rebuild the missing data out of the two remaining hard drives.
RAID 5: Similar to RAID 4, just the parity data is being written distributed over all available hard drives.
RAID 6: Similar to RAID 5. Yet four hard drives are at least required. For each data segment two parity data segments are written. RAID 6 stands a failure of two HDDs simultanously.
JBOD (Just a Bunch of Disks): Opinions are divided over this term. Some say that JBOD is/are several single partitions. Others say that the capacities of several partitions a concatenated that results in a higher capacity. Even the German and the English Wikipedia articles differ. A "Bunch" is a bundle. The hard drives (and their capacities) are bundled. The second group is right here. The hard drive capacities need not to be equal like in the other RAID levels. The controller manufacturer Adaptec also uses this definition.
The combination of several hard drives, to get data security. Also used later to increase data throughput. Meanwhile all combinations of media is commonly called RAID.
Overview over the most importand RAID levels:
RAID 0 (Striping): Data is being written devided on two or more hard drives. This RAID level produces a high data thoughput, because one hard drive can read (or write) data, while the other is positioning it's head. The hard drives must have the same capacity.
RAID 1 (Mirroring): Data is being written simultanously on two or more drives. The contents of all hard drives are identical. If a drive crashes, the computer can still work with the other hard drive(s). After changing the defect drive, the controller copies the data from the spare HDD to the new one, so that the contents are equal again.
RAID 4: This RAID level requires at least three HDDs. The first two are used for normal data, the third one is used for parity data. If a hard drive fails, the controller is able to rebuild the missing data out of the two remaining hard drives.
RAID 5: Similar to RAID 4, just the parity data is being written distributed over all available hard drives.
RAID 6: Similar to RAID 5. Yet four hard drives are at least required. For each data segment two parity data segments are written. RAID 6 stands a failure of two HDDs simultanously.
JBOD (Just a Bunch of Disks): Opinions are divided over this term. Some say that JBOD is/are several single partitions. Others say that the capacities of several partitions a concatenated that results in a higher capacity. Even the German and the English Wikipedia articles differ. A "Bunch" is a bundle. The hard drives (and their capacities) are bundled. The second group is right here. The hard drive capacities need not to be equal like in the other RAID levels. The controller manufacturer Adaptec also uses this definition.