Emc Corporation

Raju C Bopardikar

Jack Justin Stiffler

Stuart P MacEachern

Jacob Y Bast

James A Wentworth

James M Nolan

Gary A Cardone

Zdenek Radouch

David E Kaufman

Bruce D McLeod

Joris Johannes Wils

Michael J Homberg

Thomas Seidenberg

A data system architecture is described that allows multiple processing and storage resources to be connected to multiple clients so as 1) to distribute the clients' workload efficiently across the available resources; and 2) to enable scaleable expansion, both in terms of the number of clients and in the number of resources. The major features of the architecture are separate, modular, client and resource elements that can be added independently, a high-performance cross-bar data switch interconnecting these various elements, separate serial communication paths for controlling the cross-bar switch settings, separate communication paths for passing control information among the various elements and a resource utilization methodology that enables clients to distribute processing or storage tasks across all available resources, thereby eliminating 'hot spots' resulting from uneven utilization of those resources.

Method and apparatus for implementing high-performance, scaleable data processing and storage systems

Metadata that relates logical block addresses of data used by a file system with the physical block addresses at which the data is stored is maintained in nodes that are arranged into a hierarchical volume map tree that extends from a root node to a plurality of leaf nodes. A copy of the volume map tree root node is maintained in a data structure called a delta that represents the data in the covolume and the modifications to that volume map tree copy represent all additions, changes or deletions made to the volume. A copy of the data, or a new covolume, can be made by creating a new delta containing a new copy of the volume map tree root node as it existed at the time the new covolume was created. The deltas are arranged into a tree structure that represents the data in a covolume and whether the data is unchanged from a previous covolume or changed in that covolume. The delta tree structure can be used to determine whether a delta is not shared so that its covolume can be deleted. Deltas may also be arranged in local delta trees that represent changes to a particular logical is location. The local delta tree can be used to quickly locate unused locations in order to free these locations.

Method and apparatus for efficiently copying distributed data files

Each time data, in the form of data blocks protected by code checks, must be reformatted, the original data is broken into new data blocks and a new code check is calculated from, and combined with, each new data block, but the new data blocks and new code checks are both reconstituted versions of the original data blocks and the original code checks. Consequently, the data is never left without protection. In one embodiment, an ingress encoder recomputes an ingress code check from an original data block and its associated header. An egress encoder computes an egress code check from the egress header for an outgoing data block reformatted from the original data block and the ingress code check. The outgoing information is then assembled from the egress header, the outgoing data block and the newly computed egress code check.

Method and apparatus for retaining error-control code protection across block-size discontinuities

A procedure is described for determining which source to connect to which destination in a non-blocking crossbar switch through which a plurality of sources may be attempting to gain access to a plurality of destinations. To this end, a metric is dynamically associated with each source and with each destination. Matching of sources to destinations is accomplished by iteratively assigning the destination having the smallest metric of all currently unmatched destinations to the source having the smallest metric of all currently unmatched source.

Method and apparatus for determining connections in a crossbar switch

A time-weighted metric is associated with each line of data that is being held in a data cache. The value of the metric is recomputed as the lines are accessed and the metric value is used to group cache lines for paging purposes. The metrics are computed and stored and the stored metrics are maintained by linking the storage locations together in several linked lists that allow the metrics to be easily manipulated for updating purposes and for determining which metrics represent the most active cache lines. In particular, indices are maintained which identify linked lists of metrics with similar values. At regular predetermined time intervals, these indices are then used to assemble an ordered linked list of metrics corresponding to cache lines with similar metric values. This ordered list can be traversed in order to select cache lines for removal.

Method and apparatus for improving the efficiency of cache memories using chained metrics

Cache memory lines are dynamically paged out to underlying storage in accordance with their current levels of activity and are clustered for paging purposes on the same basis. Activity measures are assigned to each line when it is paged into cache; these measures are updated whenever a cached line is re-accessed. When space is needed in the cache for new lines, the activity measures are sorted based on their relative activity levels and those lines that are least active are grouped onto pages and paged out together. In this manner, the currently most active lines are retained in the cache; and lines having the same temporal characteristics and access frequencies are grouped together on the same page, thereby increasing the likelihood that when a new line is brought into the cache, the other lines that are on the same page, and hence that are brought into cache along with requested line, will themselves soon again become active.

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Carlisle, MA, United States of America

Raju C Bopardikar