Which method is used by Hitachi Unified Storage (HUS) systems to protect against loss of data in cache should a total power failure occur?

Question

Options

• AThe battery power de-stages data in cache to an on-board SSD drive.
• BThe HUS uses non-volatile cache so data is always protected.
• CThe battery power de-stages data in cache to on-board Flash memory.
• DThe HUS mirrors all cache writes to on-board SSD drives.

• A
  3% (1)
• B
  3% (1)
• C
  94% (32)

Explanation

C is correct because HUS systems use a battery backup unit (BBU) that, upon detecting a power failure, triggers a "de-staging" process - flushing dirty cache data to on-board Flash memory (NAND Flash), preserving it until power is restored.

• A is wrong because the destination is Flash memory, not an SSD drive. While SSDs use Flash internally, "SSD drive" implies a separate, discrete drive - that's not the HUS architecture.
• B is wrong because HUS does not use non-volatile RAM as its cache medium; standard DRAM cache is volatile, which is exactly why the battery-backed de-stage mechanism exists.
• D is wrong because mirroring cache writes to SSD would be a different (and more expensive) architecture - HUS does not continuously mirror all writes; it only flushes to Flash on power loss.

Memory tip: Think "Flash in a flash" - when the power flashes off, the battery gives just enough time to dump cache into Flash memory. The key word is Flash memory (not SSD, not NV-RAM, not mirroring).

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