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Special RAID Levels
RAID 5E |
RAID 5E is a variant of RAID 5 in which bands are reserved as spare. These bands are spread over the hard drive in circular manner, as is parity data. |
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RAID 5EE |
RAID 5EE is different from RAID 5 and 6.This mode is not really used in the industry. |
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RAID 5DP (Dual Parity) |
RAID 5DP (Dual Parity) is look about the same as RAID 6 but the parity drives are fixed. This RAID mode is generally used in the NAS storay bays. |
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RAID TP (Triple Parity) |
RAID TP (Triple Parity) has the same organisation as RAID 6 but this level uses 3 redundancy codes. This allows the RAID array to continue operating even when 3 hard drives fail at the same time. |
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RAID 7, RAID ADG |
This evolution of the RAID 3 level can work in an asynchronous manner. It is said to be 1.5x to 6x faster than any other RAID level. Like RAID 3, one hard drive is used to store the parity data. Each hard drive will have a SCSI (Small Computer System Interface) controller and the whole system is managed by a proprietary controller card. This card calculates the parity, manages the cache and controls the drives. This system was developed by Storage Computer Corporation and is quite expensive to implement. |
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RAID S |
RAID S is a proprietary parity RAID system from EMC Symmetrix. It appears to be similar to RAID 5 with some performance enhancements including a high-speed disk cache. |
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ServeRAID 1E |
The IBM ServeRaid 1E is a data mirroring system that allows bands to use a number of hard drives, with 2 or more pairs. The data is divided in bands that are duplicated on another hard drive of the bunch. The total capacity of the logical volume is equal to half that of the physical volume. |
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RAID-Z |
This system incorporates Sun's ZFS (Zettabyte File System, a 128-bits file system) which is a redundancy scheme similar to RAID 5. The RAID-Z avoids the write hole in RAID 5 by a rule of copy-on-write, rather than writing over old data with new data. This RAID level writes new data in a new location and then rewrites the pointer to the new data. This avoids the operations of read-modify-write for small recordings that do not require writing a "full strip". Small blocks are written into the mirror instead of being parity protected, which is possible because the file system is aware of the sub-storage structure and can allocate the extra space if necessary. The standard RAID-Z is much better than the RAID 5. However, there is also a RAID-Z2 which uses two types of parity to achieve a similar result to RAID 6 - the possibility of losing up to two hard drives without losing data. |
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