ITPEC FE Morning October 2021 Question 15

Block-level striping with distributed parity — RAID 5 stripes data in blocks and rotates the parity block across all the disks.

For each stripe, one disk holds the parity of the other disks' blocks, and which disk that is changes from stripe to stripe. Any single disk can fail and its contents are rebuilt from the others. Spreading the parity avoids one parity disk that every write must update.

The levels the options describe:

• •RAID 3: byte-level striping, one dedicated parity disk
• •RAID 4: block-level striping, one dedicated parity disk
• •RAID 5: block-level striping, parity distributed over all disks

Answer (c)

Why not others:

• •(a) and (d) — bit- or byte-level striping with a dedicated parity disk is RAID 3 (RAID 2 also stripes by bit, but protects it with Hamming-code disks)
• •(b) — block-level striping with a dedicated parity disk is RAID 4; its single parity disk becomes a write bottleneck, which RAID 5 removes

Key rule: RAID 3, 4 and 5 all spend one disk's worth of space on parity; they differ in the striping unit (byte or block) and in whether the parity sits on one disk or rotates.

System Component · AI-written, may contain errors