Low overhead methods and apparatus for shared access storage devices

A digital data processing system, comprising:

• a first node and a second node coupled for communication;
• a storage device coupled for communication with at least the first node;
• and
• a cache memory coupled to and associated with the first node, wherein the cache memory stores administrative data pertaining to files on the storage device, wherein the second node notifies the first node of changes to the administrative data pertaining to files for which the cache memory stores the administrative data, wherein a change notification identifies changes to data associated with the second node, and wherein the change notification is communicated to the first node by publishing the change notification via the second node.

A method of sharing storage access in a digital data processing system having a first node and a second node coupled for communication and a storage device coupled for communication with at least the first node, the method comprising:

• caching in a cache memory coupled to and associated with the first node, administrative data pertaining to files on the storage device;
• communicating, to the first node, changes to the administrative data pertaining to files for which the cache memory stores the administrative data, wherein a change notification identifies changes to data associated with the second node, and wherein the change notification is communicated to the first node by publishing the change notification via the second node;
• and
• determining, in the first node, whether to apply the cached data to reduce network communications for accessing a file.

A digital data processing method for access to information in a system that includes a storage device, a plurality of first nodes and a second node communicating over a communications pathway, the second node being coupled to the storage device for determining meta data for accessing file data in the storage device and the first nodes being configured for accessing file data from the storage device using the meta data, wherein the method comprises:

• caching meta data for a file accessed by the first node in a cache memory of the first node;
• providing a file application on the first node configured to get requested file data utilizing the cached data;
• storing file change notifications at the first node indicating changes that may affect the cached data, wherein the file change notifications identify changes to data associated with the second node, and wherein the file change notifications are communicated to the first node by publishing the file change notifications via the second node;
• and
• determining, based on the file change notifications, whether the file application may utilize the cached data for a requested file or whether the file application accesses the requested file from the storage device, wherein the storage device is a shared storage device between the first node and the second node.

A digital data processing system with access to information stored on a storage device, the system comprising a plurality of first nodes and a second node coupled to one another over a communications pathway, the second node being coupled to the storage device for determining meta data including block address maps to file data in the storage device, wherein the storage device is a shared storage device between the first node and the second node, and the first nodes being configured for accessing file data from the storage device using the meta data, wherein the system comprises:

• at least one first node that caches data including meta data for a file accessed by the first node;
• a file application on the first node configured to get requested file data by accessing the cached data for the file;
• and
• a file notification system that communicates a file change notification to the first node indicating changes affecting the cached data, wherein the file change notification is communicated to the first node by publishing the file change notification via the second node, wherein the file application on the first node inspects the file change notification and if the file change notification indicates that changes that affect the cached data have been made, then the requested file data is obtained from the storage device, otherwise the requested file data is directly obtained using the cached data, and wherein file accesses may be effected for an extended time with data cached at the first nodes of the digital data processing system.

A digital data processing system, comprising:

• a first node and a second node coupled for communication;
• a storage device coupled for communication with at least the first node;
• and
• a cache memory coupled to and associated with the first node, the cache memory caching administrative data pertaining to files on the storage device, wherein the second node notifies the first node of changes to the cached administrative data by publishing a change notification that indicates the changes affecting the cached administrative data, and wherein if the change notification indicates that changes that affect the cached administrative data have been made, then a file data requested by the first node is obtained from the storage device.

A method of sharing storage access in a digital data processing system having a first node and a second node coupled for communication and a storage device coupled for communication with at least the first node, the method comprising:

• caching in a cache memory coupled to and associated with the first node, administrative data pertaining to files on the storage device;
• communicating, from the second node, a change notification to the first node, wherein the change notification indicates changes affecting the cached administrative data, and wherein the change notification is published by the second node to communicate the change notification to the first node;
• receiving, by the first node, the communicated change notification;
• determining, by the first node, whether to apply the cached administrative data for accessing a file;
• accessing, by the first node, the file from the storage device if the first node determines not to apply the cached administrative data for accessing the file.

A method for accessing information stored on a storage device, wherein the storage device is shared by a plurality of first nodes and a second node, wherein the plurality of first nodes and the second node communicate over a communications pathway, wherein the second node is coupled to the storage device for determining meta data for accessing file data in the storage device, and wherein the first nodes are configured for accessing file data from the storage device using the meta data, the method comprising:

• caching meta data for a file accessed by a first node in a cache memory of the first node;
• providing a file application on the first node configured to get requested file data utilizing the cached meta data;
• storing file change notifications at the first node indicating changes that may affect the cached data, and wherein the file change notifications are communicated to the first node by publishing the file change notifications via the second node;
• and
• determining, based on the file change notifications, whether the file application may utilize the cached meta data for a requested file or whether the file application accesses the requested file from the storage device, wherein if the file change notifications indicate that changes that affect the cached meta data have been made, then the requested file is obtained from the storage device coupled to the second node.