A Question about RAID

[mmt4331]

What is RAID?? Thx.


Al & Mark

 

[jimmyz66]

RAID (redundant array of independent disks; originally redundant array of inexpensive disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, I/O operations can overlap in a balanced way, improving performance. Since multiple disks increases the mean time between failure (MTBF), storing data redundantly also increases fault-tolerance.
A RAID appears to the operating system to be a single logical hard disk. RAID employs the technique of striping, which involves partitioning each drive's storage space into units ranging from a sector (512 bytes) up to several megabytes. The stripes of all the disks are interleaved and addressed in order.

 

[miper]

Actually, assuming that two disks each have the same individual MTBF, then having two disks instead of one doubles the chance of failure. Nevertheless, when a single failure occurs, the redundancy makes the fault tolerance provided by the second disk infinitely better, so the system is perceived as being more reliable, even though it has twice the expected failure rate!

Ah, the nuances of the reliability world! It is sometimes counter-intuitive.

Reliability engineers use numerous measures to identify meaningful utility parameters to meet different customer needs. Measures include MTBF, availability, mission completion rate, servicability, etc.

ek