Caching system and method for a network storage system

Abstract

A cache system and method in accordance with the invention includes a cache near the target devices and another cache at the requesting host side so that the data traffic across the computer network is reduced. A cache updating and invalidation method are described.

Description

BACKGROUND OF THE INVENTION [0001] This invention relates generally to a system and method for storing data on computers connected by a network, such as the Internet and in particular to a caching system and method for reducing the data traffic and problems associated with network storage systems. [0002] Typical enterprise applications that run on today's Internet environment generally need to draw large amounts of data from either local or remote corporate data centers through geographically dispersed networks (e.g. Local Area Networks, Wide Area Networks, etc.). In many cases, this data traffic must share the network bandwidth with all other traffic on the network, making the delivery of data very much susceptible to network congestion. Caching is a technique of mapping frequently used data from a slow storage device, in which it is typically stored, to a higher speed storage device to achieve data access performance gains since the data can be more rapidly accessed from the highe...

AI Technical Summary

Benefits of technology

[0011] The cache systems are implemented in a manner that allows the most efficient processing of read requests to occur. Each read request initiated by a host would first be checked against the cached data in host-side cache system and be satisfied by that system if the requested data is present. If the host-side cache could not satisfy the read request, the read request is sent out to the storage-side cache. If a cache hit occurs at the storage-side cache system, the read request is satisfied by that system. If both cache systems fail to generate a cache hit for the read request then the request is forwarded to the target storage device to satisfy the read request. Thus, the slow access-time target storage device is only accessed to satisfy a read request if both the host-side cache system and the storage-side cache system cannot satisfy the read request. Thus, network traffic is reduced if a host-side cache hit occurs or target storage latency is reduced if the storage-side cache hit occurs. In the case where both caches do not contain the data, when the data is transmitted from the target storage device back to the initiating host, the data would preferably pass through and be stored in both the host-side cache as well as the storage-side cache for future use.

[0013] Because of the way the cache systems may be deployed, the cache systems may be installed in strategic distributed locations throughout any arbitrary network between any hosts requesting data and any target storage devices providing the data. This network may be composed of local area networks (LANs), metropolitan area networks (MANs), wide area networks (WANs), storage area networks (SANs), or any combination of these network types. Therefore, regardless of the physical locations of the requesting hosts or the target devices, the two system caches on the data path between the requesting host and the target device in accordance with the invention will greatly increase the chance of being able to serve the requests with reduced network traffic and / or decreased access latency.

[0015] At the target storage device side, a cache system keeps a large cache for all attached storage devices in the local storage network. Data requests from outside the local storage network can potentially be satisfied by drawing data from the cache and avoiding local accesses to the local storage devices. At the other end of the intermediate geographically dispersed network, another large cache is kept in the cache system for storing data that have been accessed by all local hosts in the past. Thus, future read requests for the same data will be satisfied by this cache system thereby totally eliminating traffic over the intermediate network.

[0016] Cache data invalidation, in accordance with this invention, may be initiated when one cache system detects a write request. The cache manager program automatically sends out messages to all other cache systems on the network for their cache managers to check and invalidate the blocks of data being stored in originator's cache. When writing a small amount of data, instead of invalidating the system caches on the network, it might be more efficient to just update those caches with the data. The cache system allows users to set a threshold value so that when the amount of data being written is smaller than that threshold value, the system may perform a cache update otherwise it may perform cache invalidation for all cache systems on the network.

Problems solved by technology

In addition, data frequently accessed by a group of hosts / clients are cached in the system deployed near the requesting host devices.

Thus, the slow access-time target storage device is only accessed to satisfy a read request if both the host-side cache system and the storage-side cache system cannot satisfy the read request.

The caching system does not support separate write cache.

However, when a write request occurs, the system on the storage side will use the written data to refresh its cache and the cache system on the host side will either use the data to refresh its cache or to simply invalidate the same data in the cache if it was already there.

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