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System Architecture and Reliability

RAID 5 is built from four disks with a capacity of 4 TB each. Which is the capacity available for storing data?

  1. A8 TB
  2. B12 TB
  3. C16 TB
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Answer: B. 12 TB

RAID 5 writes data and parity distributed across all the disks and uses one disk's worth of capacity for parity. The capacity available for data is therefore (4 − 1) × 4 TB = 12 TB, and if one disk fails, the lost data can be restored from the data and parity on the remaining disks. 8 TB is the capacity for RAID 1 or RAID 10, which halve the capacity, and 16 TB is the capacity for RAID 0, which has no redundancy.

  • A. This halves the capacity, as with mirroring (RAID 1 or RAID 10).
  • B. Correct. (4 − 1) × 4 TB = 12 TB.
  • C. This is the capacity of all four disks, the value for RAID 0 with no redundancy.
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More System Architecture and Reliability questions

  1. RAID 6 is built from six disks with a capacity of 8 TB each. Which is the correct combination of the capacity available for storing data and the number of disks that can fail at the same time without losing data?
  2. In a RAID 10 array of four disks (two mirrored pairs, striped across the two pairs), two of the four disks fail at the same time. If every pair of disks is equally likely to be the one that fails, which is the probability that data is lost?
  3. RAID 5 is built from four disks, each capable of 200 random input/output operations per second (IOPS). Each small random write requires four I/O operations in total: reading the old data and the old parity, and writing the new data and the new parity; cache effects are ignored. When only writes are performed, which is the number of writes the whole RAID 5 array can process?
  4. Which describes a differential backup?
  5. A full backup is taken every Sunday night, and an incremental backup is taken every night from Monday to Saturday. A failure occurs at midday on Thursday, and it is decided to restore the data to the point of Wednesday night's backup. Which is the number of backups used for the restore?