Frostmere 2.1: multi-backend and chunk-level dedup
2026-04-20 · Ava Lindqvist
Frostmere 2.1 introduces multi-backend support — you can now span a single archive across Backblaze B2, S3 Glacier, and local storage simultaneously.
Multi-backend routing
The routing policy lives in a TOML config block. The default policy mirrors everything to all configured backends. A tiered policy can route recent data to B2 (fast, cheap retrieval) and older data to S3 Glacier (slow, cheapest storage) automatically based on age.
Backends are addressed by name in the config; the CLI accepts --dest backend:path syntax for targeting specific backends on the command line.
Chunk-level deduplication
Frostmere now uses content-defined chunking (FastCDC algorithm) to split files before hashing. This means that inserting a frame in the middle of a video or adding lines to a log file doesn't invalidate all subsequent chunks — only the affected chunks need to be re-uploaded.
For workloads with lots of small edits to large files, dedup rates above 80% are common. For mostly-new data the overhead is negligible.
Also: Why content-addressed storage changed how I think about backups