The Dell Avamar client needs to backup a file and has performed sticky-byte factoring. This results in the following: Seven (7) chunks that will compress at 30% Four (4) that will compress at 23% Two (2) chunks at 50% compression How many chunks will be compressed prior to hashing?

Avamar first tests each chunk’s compressibility. If the compressed size is 25 % (or more) smaller than the original, the chunk is compressed before its hash is calculated.
• 7 chunks compressible by 30 % (>25 %)
• 4 chunks compressible by 23 % (<25 %)
• 2 chunks compressible by 50 % (>25 %) Therefore, 7 + 2 = 9 chunks are compressed prior to hashing.

A. 4 – only counts the chunks at 23 %; these are below the compression threshold.
B. 7 – ignores the two 50 %-compressible chunks that also meet the threshold.
D. 13 – assumes every chunk is compressed; those at 23 % are not.

1. Dell EMC “Avamar Deduplication and Compression Technical Note” (H12762-A), §3.2, p.6 – “Chunks are stored in compressed form only when the compressed size is ≤75 % of the original (≥25 % reduction).”

2. Dell EMC Avamar 7.0 System Administration Guide, p.120 – description of client-side chunk compression threshold prior to hash generation.

3. Dell Technologies “Avamar Product Architecture Overview” Rev C, p.14 – workflow diagram showing ‘Compress (if ≥25 % gain) → Hash’.