Write buffering (aka write-back cache) is optionally used with magnetic HDDs. StorPool supports Intel Optane drives for persistent write-back cache, the use of a small partition on large capacity Pool NVMe drives, or the use of an LSI CacheVault(supercap) or BBU. This effectively protects against data loss even in the events of full power outage of the entire data center.
In low cost / low performance use-cases write buffering for HDDs can be disabled, thus removing the requirement for a write-back cache device, at the cost of increased write latency (write operations wait for the HDD media).
Datacenter-grade SSDs and NVMe have integrated power-loss protection which StorPool uses, so for these types of devices StorPool doesnt require external write buffering.
StorPool, StorPool [SDS]/19.01, x86
Persistent Write Buffer, Reads/Writes, Data Availability