RAID disks

RAID disk reading

Many disks are now being sold as a RAID (Redundant Array or Inexpensive Disks). These may be standalone, or as a NAS system. CnW has an option to allow these disks to be read. Up to 12 disks in a RAID can be supported, and they can be a mixture of physical disks, or disk inage files.

A RAID was typically designed for security, a disk drive (or in some cases) multiple drives could fail, and all data would be readable. However, RAID-0 does exist that offers no security at all, and can often be argued makes loss of data twice as likely.

On all types of RAID, data is stored in stripes of a fixed size. A stripe if often 32KB or 64KB in size. For RAID 5 and RAID 6 there are stripes that just contain error correction codes for other disks stripes, which allows for recovery after a single disk failure. RAID-1 does not have stripes, but is a complete mirror of two disks. RAID-0 is just data in stripes, but no error correction or recovery possible. RAID-0 can produce a fast disk, but a single failure will result in 50% of data being lost. If the stripe is 32K, then only some files of less than 32K will be readable.

The CnW RAID option will read disks that are RAID-0 and RAID-5. It will also handle disks that start with a
RAID-1 section, where there may be multiple (small) partitions of duplicated operating system files.

● RAID-0 has no redundancy - a single failure and all is lost
● RAID-1, a single disk may fail
● RAID-5 This is 3 or disks, a single disk may fail and no data lost. 2 disk failures is normally all data lost
● RAID-6. This is 4 disks or more. 2 disks can fail and no data lost - not supported by CnW