cache-flush · shipping · also write cache flush, REQ_PREFLUSH

Storage cache flush

A storage cache flush requests persistence of writes buffered in the addressed storage stack, with its coverage and ordering defined by that interface.

In the Linux block layer, REQ_PREFLUSH makes previously completed writes persistent before an accompanying I/O starts; it can also be issued without a data payload. REQ_FUA instead covers persistence of the flagged write before its completion, and both flags may be combined. This block-level operation does not submit data still held only in an application buffer or establish multi-file transaction atomicity. Device-mapper layers must propagate the required persistence semantics.

Relations

related

force-unit-access, write-back-cache, write-through-cache, fsync, persistence-ordering

Advantages

• Provides a persistence boundary for earlier completed writes in a stack that honors the request. [1]

Limitations

• A successful lower-layer flush does not certify an application's complete recovery protocol. [1, 3]

Citations

1. Linux kernel documentation. Explicit volatile write back cache control: REQ_PREFLUSH and REQ_FUA. (accessed 2026-10-12)
2. Linux kernel documentation. Device-mapper cache: operating modes and on-disk metadata. (accessed 2026-10-12)
3. NFS stable writes: what COMMIT, flush and FUA actually promise (accessed 2026-10-12)

JSON: /data/terms/cache-flush.json