2. 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

3. Failure of any drive causes the loss of all data in the array Very high performance No overhead for writing fault tolerance data

4. 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

5. 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

6. Transfer rate per block is nearly equal to single disks Capacity is half the total capacity of the drives in the array

7. No rebuild is necessary if a disk fails. Data is simply copied to the replacement disk

8. Data Transfer Data 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

9. Data Transfer Data Word Extremely high transfer rates possible Requires hard drives with specialized ECC circuitry Expensive

10. Data Transfer Data Word Ratio of data disks to ECC disks decreases with increasing transfer rate requirements Cost is very high - not economical or practical

11. Data Transfer Data Word Relatively simple controller design Transaction rate is the same as a simple disk at most (with spindle synchronization)

12. Data Transfer Data Word “On the fly” data error correction Not implemented commercially All disks in the array must be accessed for every good read and write

13. High read and write transfer rate (with synchronized spindles) Synchronized spindles mean only one transaction processed at a time

14. Transaction rate the same as a single disk at best Disk failure has low impact on throughput

15. Good for large sequential data transfers Not a good solution for random access and small data transfers

16. 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)

17. 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

18. Data Transfer Spindles do not need to be synchronized All drives are not necessarily involved in a read or write (Independent access)

19. Highest read transaction rate Medium write transaction rate Good aggregate transfer rate

20. Individual block data transfer rate the same as an individual disk Disk failure has a medium impact throughout

21. Spindles not synchronized Data striped at the block level

22. Data striped on block level Parity generated just like Raid 5. Second set of parity is calculated and also written across all the drives

23. Very reliable Can sustain two simultaneous drive failures

24. Very high controller overhead to compute parity addresses Poor write performance Capacity is N-2 drives

25. 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

26. 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

27. Data Transfer Expensive – capacity is half the total capacity of the disks Excellent solution for sites that want RAID 1, but need increased performance

28. Data Transfer High performance is a result equal distribution of I/O load Reduces hot spotting in the disks, continued fill of the drive buffers for high sustained transfer rates on large transfers, multiple spindle access for high performance random transactions