A backup that eats the processor slows the sites down while it runs, and the customer notices.
Of the three steps the engine runs on every chunk of a file (fingerprint, compression and encryption), which weighs most on the processor? Is any algorithm worth switching?
Result
8 msper MB for compression, versus 2.4 ms for the hash and 1.1 ms for encryption, on one core
~17%more throughput if the hash becomes BLAKE3
Why it matters to whoever runs the server
Knowing which step weighs most shows where to save: compression costs 8 ms per MB on one core; encryption, 1.1 ms. Encrypting the backup costs the server almost nothing extra.
The algorithm is a trade between processor and storage space: s2 is 8× faster but takes about 27% more space. Salvo keeps light compression as the default.
Cost of each step on one core, with the defaultsMilliseconds per MB · lower is better
Compression (zstd-fastest)
8.1 ms
Hash (BLAKE2B)
2.4 ms
Encryption (AES-256-GCM)
1.1 ms
Source: Salvo Lab · Salvo engine benchmark, processor only · Oct 15, 2026
See the data as a table
Algorithm
1 core
All cores
Hash BLAKE3
1.5 GB/s
18.7 GB/s
Hash BLAKE2B (default)
418 MB/s
5.7 GB/s
Encryption AES-256-GCM (default)
900 MB/s
7.7 GB/s
Encryption ChaCha20-Poly1305
654 MB/s
7.4 GB/s
Compression zstd-fastest (default), 15.4% of the size
123 MB/s
848 MB/s
Compression zstd, 13% of the size
89 MB/s
650 MB/s
Compression s2, 19.6% of the size
1 GB/s
2.9 GB/s
Method
Test server with a Xeon E5-2698 v4 (2.2 GHz, 18 cores).
The Salvo engine’s benchmark tool, measuring only the processor, with no disk and no network.
Compression was measured on 256 MB of real code from a WordPress site.
What we decided
We keep AES-256 and zstd-fastest. Before switching the default hash to BLAKE3, we’ll measure it on a new repository: the hash is fixed when the repository is created. s2 is 8× faster but takes ~27% more space; it may become an option for those who prefer speed over space.
?
What we don’t know yetThis is a pure processor measurement: in a real backup, reading the disk and walking thousands of files also weighs in. The sample is only site code, mostly text; whole accounts, with images and email, compress less. And single-core numbers vary with server load (BLAKE3 gave 0.9 to 1.5 GB/s across two runs); the ranking between algorithms held.
Want to see Salvo on your server?Join the beta waitlist. We’ll let you know when there’s a spot.