English
Menu

System Architecture and Reliability

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?

  1. A32 TB, up to 2 disks
  2. B40 TB, up to 1 disk
  3. C48 TB, up to 2 disks
Show answer and explanation

Answer: A. 32 TB, up to 2 disks

RAID 6 writes two kinds of parity distributed across the disks and uses two disks' worth of capacity for parity. The capacity available for data is (6 − 2) × 8 TB = 32 TB, and no data is lost even if up to two disks fail at the same time. As disk capacities grow, recovering (rebuilding) from one disk failure takes longer and the risk of another disk failing in the meantime increases, so RAID 6 is often chosen over RAID 5.

  • A. Correct. (6 − 2) × 8 TB = 32 TB, and it tolerates two disk failures.
  • B. This is the value for RAID 5. Parity takes one disk, so it tolerates only one disk failure.
  • C. This is the capacity of all six disks and does not subtract the parity.
Practice this topic Back to topic

Related calculators

RAID Capacity CalculatorCalculate usable capacity, capacity efficiency, how many disk failures can be tolerated and the chance of data loss for RAID 0, 1, 5, 6 and 10 from the number and size of disksAvailability CalculatorCompute availability from MTBF and MTTR, and the availability and annual downtime of systems built from series, parallel and k-out-of-n units

Books on System Architecture and Reliability Ad

As an Amazon Associate I earn from qualifying purchases.

More System Architecture and Reliability questions

  1. 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?
  2. 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?
  3. Which describes a differential backup?
  4. 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?
  5. In a system with 500 GB of data in total, a full backup is taken every Sunday, and a differential backup is taken every night from Monday to Saturday. Each day, 20 GB of other data that had not been changed until then is changed. Which is the total size of the six differential backups from Monday to Saturday?