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Endurant cache (EC) was introduced in OneFS 7.1.1 and was aimed at reducing the latency of synchronous (immediate or stable write) small block random writes. The primary goal of this feature was to help with latency of VMware-type workloads on PowerScale storage.
By default, stable storage is written to disk, and a synchronous write requires the storage system to write to stable storage. Because the write is smaller than the Reed Solomon stripe, this causes a READ/WRITE/MODIFY penalty and impacts response time.
EC effectively works around this process by writing the small write to a small part on the journal that is protected. EC then has to de-stage these writes to disk over time. If multiple writes are issued to the same stripe, the de-staging of these writes is more efficient since the R/W/M penalty is only paid once.
An issue occurs when the EC space is not large enough. While EC helps with bursts, continuous traffic of small-block writes may cause it to constantly catch up, and this can result in lower performance compared to not using EC.
EC can be managed on and off globally and tuned on or off per directory.
The recommendation is to turn this off globally for EDA workloads.
To disable globally, use below command.
isi_sysctl_cluster efs.bam.ec.mode=0