A storage administrator wants to implement FAST Cache with a capacity of 1.6 TB to an existing Dell Unity XT 680 array. How many drives must the administrator use to implement this configuration?

Question

Options

• A4
• B16
• C2
• D8

• A
  5% (1)
• B
  9% (2)
• C
  9% (2)
• D
  77% (17)

Explanation

Option D (8 drives) is correct because Dell Unity XT FAST Cache uses SSDs configured in mirrored pairs (RAID 1), and the Unity XT 680 employs 400 GB SSDs for this purpose. Eight drives form four mirrored pairs, delivering 4 × 400 GB = 1.6 TB of usable FAST Cache - exactly the target capacity.

Why the distractors are wrong:

• A (4 drives): Only 2 mirrored pairs × 400 GB = 800 GB - half the required capacity.
• C (2 drives): Just 1 mirrored pair × 400 GB = 400 GB - far too little.
• B (16 drives): Eight mirrored pairs × 400 GB = 3.2 TB - double the required capacity and wasteful.

Memory tip: Think "FAST Cache = mirrored pairs." Divide the target capacity by the individual SSD size (400 GB) to get the number of pairs, then multiply by 2 to get drives. For 1.6 TB: 1600 ÷ 400 = 4 pairs → 4 × 2 = 8 drives.

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