Two or more disks Capacity is the same as the total capacity of the drives in the array No fault tolerance-risk of data loss is proportional to the number of drives in the array
Dec 26, 2015
Two or more disks
Capacity is the same as the total capacity of the drives in the array
No fault tolerance-risk of data loss is proportional to the number of drives in the array
Failure of any drive causes the loss of all data in the array
Very high performance
No overhead for writing fault tolerance data
Used where performance is important and occasional data loss is acceptable
Implemented in some operating systems. Also available in third party software and hardware packages
Can do one write or two simultaneous reads per mirrored pair
Same write transaction rate as single disks
Twice the read transaction rate as single disks
Transfer rate per block is nearly equal to single disks
Capacity is half the total capacity of the drives in the array
Data TransferData Word
ECC stands for Error Correction Code
Striping is performed at the bit level
High ratio of ECC disks to data disk with smaller word sizes
Data TransferData Word
Extremely high transfer rates possible
Requires hard drives with specialized ECC circuitry
Expensive
Data TransferData Word
Ratio of data disks to ECC disks decreases with increasing transfer rate requirements
Cost is very high - not economical or practical
Data TransferData Word
Relatively simple controller design
Transaction rate is the same as a simple disk at most (with spindle synchronization)
Data TransferData Word
“On the fly” data error correction
Not implemented commercially
All disks in the array must be accessed for every good read and write
High read and write transfer rate (with synchronized spindles)
Synchronized spindles mean only one transaction processed at a time
Good for large sequential data transfers
Not a good solution for random access and small data transfers
Capacity is total capacity of the disks minus the capacity of one disk
All disks in the array must be accessed for every read and write (Parallel access)
Data Transfer
Striping is at the block level, so RAID 4 is somewhat more efficient than RAID 3
High read transaction rate
High aggregate read transfer rate
Data Transfer
Spindles do not need to be synchronized
All drives are not necessarily involved in a read or write (Independent access)
Individual block data transfer rate the same as an individual disk
Disk failure has a medium impact throughout
Data striped on block level
Parity generated just like Raid 5. Second set of parity is calculated and also written across all the drives
Very high controller overhead to compute parity addresses
Poor write performance
Capacity is N-2 drives
Data Transfer
Implemented as a RAID 0 array whose elements are RAID 1 array
Same level of fault tolerance as RAID 1
Same overhead for fault tolerance as RAID 1
Data Transfer
High I/O rates are achieved by striping RAID 1 arrays
All drives must move in parallel to proper track, lowering sustained performance
Data Transfer
Expensive – capacity is half the total capacity of the disks
Excellent solution for sites that want RAID 1, but need increased performance