hesela.devArmorCache
ArmorCache is an HDD cache-protection feature that uses OptiNAND flash to preserve buffered user writes during emergency power loss on supported drives.
Spindle rotational energy powers transfer of buffered writes into iNAND after external power fails, in WCE and WCD modes. Host queue depth 1 can coexist with a larger internal backlog after command completions. [1]
A SAS drive specification permits SYNCHRONIZE CACHE completion after persistence in iNAND when write caching and protection are enabled; that need not mean a platter commit. [2] Device protection is not a transaction protocol and cannot preserve data still in upstream caches. [3]
Relations
- related
- optinand, power-loss-protection, write-back-cache, cache-flush, force-unit-access
Citations
- Western Digital. ArmorCache Write Cache Data Protection, May 2022, pp. 1-3; host and internal queue depth on p. 3.
- Western Digital. Ultrastar DC HC570 SAS specification, revision 1.2, 21 September 2023, section 6.5.2, p. 36.
- Linux kernel documentation. Explicit volatile write back cache control: REQ_PREFLUSH, REQ_FUA and driver responsibilities.
Further reading
Sources & caveats
- ArmorCache is a Western Digital feature; support and performance depend on model, firmware, configuration and workload.
- The HC570 SAS revision 1.2 example specifies up to 128 MiB of protected user data. It is a model-scoped protection capacity, not total DRAM or a transaction limit. [2]