How is XOR optimization implemented on an ECS geo-active replication group containing three sites?

Question

Options

• APrimary copy of chunk A on VDC1
• BPrimary copy of chunk A on VDC1
• CPrimary copy of chunk A on VDC1
• DPrimary copy of chunk A on VDC1

• A
  7% (3)
• B
  13% (6)
• C
  78% (36)
• D
  2% (1)

Explanation

Note: The four answer choices appear identical as presented - this is likely a formatting issue in the source material. I'll explain based on the known ECS 3-site XOR optimization concept, which is what this question tests.

In a 3-site ECS geo-active replication group, XOR optimization reduces storage overhead by replacing a third full data copy with an XOR parity chunk. Option C correctly describes the optimized layout: VDC1 holds the primary copy of chunk A, VDC2 holds the primary copy of chunk B, and VDC3 holds the XOR of A and B - meaning any single site failure allows full data reconstruction from the remaining two sites.

The distractors (A, B, D) likely represent incorrect chunk placements - such as storing two copies of the same chunk on different VDCs, placing the XOR parity on the same VDC as a source chunk, or reverting to a full third replica - all of which either waste capacity or break the reconstruction guarantee.

The key distinguishing detail is that XOR lives on the third VDC and is derived from chunks on the other two VDCs, not a copy of either.

Memory tip: Think "two sources, one derived" - VDC1 and VDC2 each own a unique data chunk, and VDC3 holds their XOR. If any one site goes down, the surviving two sites always have enough information to rebuild everything.

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