The most popular (i.e., commercially successful) RAID levels are 1 and 5. Why?

Question

What will be an ideal response?

Answer 1

RAID level 1 is the simplest RAID arrangement that offers error protection. In level 1 RAID disks are simply
replicated or duplicated; that is, two drives store exactly the same data. This is also called data mirroring.
Clearly, if one drive fails, the other drive still contains the correct data. Moreover, a failure of one disk does
not require the re?creation of data that is distributed across several drives. Level 1 RAID has a faster read time
than other forms of RAID because both drives can be accessed in parallel and data accepted from the first
drive to access it. The disadvantage of level 1 RAID is its relatively high cost. The storage capacity is halved
because data is duplicated. However, this is acceptable for applications requiring a high level of reliability.

RAID level 5 uses three or more drives and the data is distributed across all the drives of an array. That is, the
array appears as a single large drive. A block of data that is distributed across all of the disks contains both
the actual data and the parity information that can be used to correct errors. This parity information is also
distributed across the drives (unlike in RAID level 4 a single drive is dedicated to parity storage). If there are n
drives in a level 5 RAID array, the effective capacity is n ? 1 drives because of the need to store parity
information. Should one drive fail, the information can be recovered using the parity information. However, it
may take a considerable time to recreate the information lost on the failed drive. The level 5 RAID system has
a good fault tolerance because it can withstand the loss of one drive, is relatively cheap to implement, and
has a good storage efficiency of (n ? 1)/n where n is the number of drives.