DEA-1TT5 RAID and Data Protection 2 — Questions and Answers
Question 1: What happens to a RAID 5 array when a disk fails?
- Data is immediately lost and the array goes offline
- The array operates in a degraded mode using parity to reconstruct the missing data on reads (Correct answer)
- The array automatically shifts to RAID 1
- All remaining disks mirror the lost data instantly
Correct answer: The array operates in a degraded mode using parity to reconstruct the missing data on reads
A RAID 5 array with one failed disk operates in 'degraded mode,' recalculating missing data on-the-fly using parity during reads until a replacement disk is rebuilt.
Question 2: What is 'RAID rebuild' and why can it be risky?
- Reconfiguring RAID levels, which risks overwriting user data
- Reconstructing a failed disk's data onto a replacement disk, which stresses remaining drives and risks a second failure (Correct answer)
- Upgrading controller firmware while data is online
- Moving RAID sets between storage arrays
Correct answer: Reconstructing a failed disk's data onto a replacement disk, which stresses remaining drives and risks a second failure
RAID rebuild reconstructs lost data onto a replacement drive by reading all remaining drives intensively, which increases the risk of uncovering another drive's latent errors during the process.
Question 3: Which RAID level mirrors data across two disks, providing full redundancy with 50% usable capacity?
- RAID 0
- RAID 5
- RAID 1 (Correct answer)
- RAID 6
Correct answer: RAID 1
RAID 1 writes identical copies of data to two disks simultaneously, meaning if one disk fails, an exact duplicate exists on the other disk.
Question 4: What is 'copyback' in a RAID context?
- Copying data from cache back to disk after a write
- Migrating rebuilt data from a hot spare back to a new permanent replacement disk (Correct answer)
- Backing up data from the primary to a secondary array
- Reverting a RAID configuration to a previous state
Correct answer: Migrating rebuilt data from a hot spare back to a new permanent replacement disk
Copyback is the process of moving data from a hot spare (used during an emergency rebuild) back to a new permanent replacement disk once it has been physically installed.
Question 5: How many minimum disks are required to implement RAID 5?
- 2
- 3 (Correct answer)
- 4
- 5
Correct answer: 3
RAID 5 requires a minimum of 3 disks: at least 2 for data striping and 1 disk's worth of distributed parity across all drives.
Question 6: What does 'write hole' refer to in RAID 5 environments?
- A physical hole drilled in the disk platter during manufacturing
- A data consistency issue where a system crash during a write leaves data and parity out of sync (Correct answer)
- An unallocated region of the disk not included in any RAID set
- A performance bottleneck caused by excessive parity calculations
Correct answer: A data consistency issue where a system crash during a write leaves data and parity out of sync
A write hole occurs when a power failure interrupts a RAID 5 write mid-operation, leaving data and parity blocks inconsistent, which can cause data corruption on subsequent reads.
DEA-1TT5 RAID and Data Protection 2
What happens to a RAID 5 array when a disk fails?