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System Architecture and Reliability

Which describes RAID 1?

  1. AData is divided and written across several disks (striping) to speed up reads and writes, but there is no redundancy
  2. BThe same data is written to two disks (mirroring), so no data is lost if one disk fails
  3. CData and parity for error correction are written distributed across several disks, so data can be restored if one disk fails
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Answer: B. The same data is written to two disks (mirroring), so no data is lost if one disk fails

RAID 1 is mirroring, which writes the same data to two disks, so if one disk fails, processing can continue with the data on the other. The capacity available for data is half the total of the two disks. Striping alone with no redundancy is RAID 0, and writing parity distributed across disks is RAID 5. Note that RAID protects against disk failures; data deleted by mistake or encrypted by ransomware is reflected on both disks, so RAID is no substitute for backups.

  • A. This describes RAID 0. If even one disk fails, data is lost.
  • B. Correct. Mirroring tolerates the failure of one disk.
  • C. This describes RAID 5.
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More System Architecture and Reliability questions

  1. RAID 5 is built from four disks with a capacity of 4 TB each. Which is the capacity available for storing data?
  2. 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?
  3. 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?
  4. 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?
  5. Which describes a differential backup?