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Talk by Shailendra Tripathi of Tegile at OpenZFS Developer Summit 2017:

Static assignment of SSD or high performance media by partitioning into sets for logical or physical use, (e.g. log, read cache, and, metadata) is very inefficient utilization of either the IOPS and/or the capacity. Largely bi-modal usage underscores the issue requiring different mechanism to increase the value addition. For example, in filesystem usage, logging and metadata access can bi-modal. The bi-modal behavior can be driven by the application as well. For example, new data write workloads may stress more on log and cache whereas regular typical read/write may stress more on metadata IOPS. iFlash architecture pools the fast media and provides different data protection, shared capacity, shared IOPS, and, QoS on top of it. Additionally, the infrastructure supports the mechanism to dynamically adjust the resources between competing classes automatically and dynamically while providing the different data protection, and, allocation mechanism for classes on top of this pool.