Extending cache for an external storage system into individual servers

摘要

Mechanisms are provided for extending cache for an external storage system into individual servers. Certain servers may have cards with cache in the form of dynamic random access memory (DRAM) and non-volatile storage, such as flash memory or solid-state drives (SSDs), which may be viewed as actual extensions of the external storage system. In this way, the storage system is distributed across the storage area network (SAN) into various servers. Several new semantics are used in communication between the cards and the storage system to keep the read caches coherent.

主权项

1. A method, in a data processing system, for extending cache for a storage system in a storage area network, the method comprising:
responsive to a server data processing system performing a write operation to write a first portion of data to an external storage system, storing a copy of the first portion of data in a non-volatile memory of an extended cache card and updating a directory bit map in the extended cache card, wherein the extended cache card comprises a host side interface through which the extended cache card connects directly to a bus of the server data processing system, a storage side interface through which the extended cache card connects to a storage area network, and the non-volatile memory, wherein the server data processing system connects to the external storage system via the storage area network, and wherein the directory bit map keeps a record of which servers having extended cache cards store particular portions of data; responsive to the server data processing system performing a read operation to read a second portion of data from the external storage system, determining whether the extended cache card stores an up-to-date copy of the second portion of data; and responsive to a determination that the extended cache card stores an up-to-date copy of the second portion of data, sending the copy of the second portion of data from the extended cache card to the server data processing system.