Expand description
2026-09-25: CascadeBackend: a write-back cache of groups in pinned host
memory (T1) in front of another StorageBackend. Writes land in T1; when
T1 is full, the least recently used group is written down to the backing.
Reads copy T1 hits to the device and forward misses to the backing. No
tier transforms bytes.
Owner: metrale-storage KV tier. Invariants:
- A read of a group resident in T1 is served from T1; misses are not copied into T1.
- A write waits for the event recorded after the last async hit copies before it overwrites a slot.