A company needs to expand their dynamic pool by 5 TB. The current dynamic pool consists of 63 3.8 TB SSDs that are configured for RAID5 (4+1). What is the minimum number of drives needed for the…

Question

Options

• A1
• B5
• C6
• D7

• A
  3% (1)
• B
  10% (3)
• C
  80% (24)
• D
  7% (2)

Explanation

Option C (6 drives) is correct because expanding a RAID5 (4+1) dynamic pool requires a minimum of one complete RAID group - 5 drives (4 data + 1 parity) - plus 1 dedicated hot spare drive to maintain fault tolerance during a potential drive failure after expansion, totaling 6 drives.

Why the distractors are wrong:

• A (1): A single drive cannot form any RAID5 group; RAID5 (4+1) requires at minimum 5 drives to function.
• B (5): Five drives can form one RAID5 (4+1) group with 4 × 3.8 TB = 15.2 TB of usable capacity (exceeding the 5 TB requirement), but this leaves no hot spare - any drive failure would leave the new pool segment unprotected with no rebuild target.
• D (7): This exceeds the minimum; the 6th drive satisfies the hot spare requirement, so a 7th is unnecessary to meet the minimum.

Memory tip: Think "RAID group + 1 guardian." For RAID5 (4+1), your RAID group already uses the +1 slot for parity, so you need one extra drive as the hot spare - always add the RAID group size plus one when calculating pool expansion minimums.

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