Multi-Leveled Cache Management in a Hybrid Storage System

摘要

A hybrid storage system is described having a mixture of different types of storage devices comprising rotational drives, flash devices, SDRAM, and SRAM. The rotational drives are used as the main storage, providing lowest cost per unit of storage memory. Flash memory is used as a higher-level cache for rotational drives. Methods for managing multiple levels of cache for this storage system is provided having a very fast Level 1 cache which consists of volatile memory (SRAM or SDRAM), and a non-volatile Level 2 cache using an array of flash devices. It describes a method of distributing the data across the rotational drives to make caching more efficient. It also describes efficient techniques for flushing data from L1 cache and L2 cache to the rotational drives, taking advantage of concurrent flash devices operations, concurrent rotational drive operations, and maximizing sequential access types in the rotational drives rather than random accesses which are relatively slower. Methods provided here may be extended for systems that have more than two cache levels.

主权项

1. Apparatus for storing data comprising:
a first cache for storing data; wherein the first cache comprises volatile memory; a second cache for storing data, the second cache being in communication with the first cache; wherein the second cache comprises non-volatile memory; a first group of IO interface DMA controllers for communicating between the first cache and a plurality of external host systems; a second group of IO interface DMA controllers for communicating between the first cache and a plurality of external mechanical disk drives; and a first flash interface DMA controller for communicating between the second cache and the first cache.