Definition
Plain language
A layered filesystem that saves what changed without copying everything else.
As stated in the literature
DeltaBox's filesystem component, an OverlayFS-derived stack on XFS with reflinks that allows runtime layer pivots and incremental snapshots whose disk cost scales with the actual delta.
Why it matters: It keeps frequent snapshots cheap enough to take routinely, which is what makes always-on rollback practical for long agent runs.
For example, if an agent writes a 4KB log entry to a 10GB log file, DeltaFS records only the 4KB change rather than copying the whole file.
Heard on the show
“So the filesystem half of this is called DeltaFS, and the analogy that makes it click is a stack of transparent acetate sheets.”Episode 068 — The OS Trick That Makes Tree Search Practical for Coding Agents