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CompTIA Linux+ (XK0-006)System ManagementHard

A storage array is configured as RAID 5 using four disks, each with 2TB of raw capacity. What is the approximate usable storage capacity of this array?

  1. A8 TB
  2. B2 TB
  3. C4 TB
  4. D6 TB
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Correct answer: D. 6 TB

RAID 5 uses distributed parity equivalent to one disk's worth of capacity across the array. Usable capacity = (n-1) × disk size = (4-1) × 2TB = 3 × 2TB = 6TB.

Why the other options are wrong

  • A. 8TB would be the raw total with no parity overhead accounted for (as in RAID 0).
  • B. 2TB would only be correct for a RAID 1 mirror using two of these disks, not a four-disk RAID 5 array.
  • C. 4TB would correspond to a RAID configuration losing two disks' worth of capacity, like RAID 6 with these numbers minus one more disk, not RAID 5.

RAID 5 Capacity Calculation

RAID 5 stripes data with distributed parity equal to one disk's capacity, so usable space equals (number of disks - 1) multiplied by the size of one disk.

  • Formula: usable = (n-1) × disk size
  • RAID 5 tolerates failure of exactly one disk
  • Requires a minimum of three disks

Memory trick: 'RAID 5 always gives back one disk to the parity gods.'

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