Emc Corporation

Daniel Lambright

Natan Vishlitzky

Yuval Ofek

Adi Ofer

Josef Ezra

Sachin More

Yechiel Yochai

Yedidia Atzmony

Described are techniques and criteria used in connection with cache management. The cache may be organized as a plurality of memory banks in which each memory bank includes a plurality of slots. Each memory bank has an associate control slot that includes groups of extents of tags. Each cache slot has a corresponding tag that includes a bit value indicating the availability of the associated cache slot, and a time stamp indicating the last time the data in the slot was used. The cache may be shared by multiple processors. Exclusive access of the cache slots is implemented using an atomic compare and swap instruction. The time stamp of slots in the cache may be adjusted to indicate ages of slots affecting the amount of time a particular portion of data remains in the cache.

Cache management via statistically adjusted time stamp queue

Described are techniques used in connection with cache management. Data included in a cache slot is put 'on parole' with a first cache hit while waiting for subsequent cache hits. If a subsequent hit is received to the cache slot, it remains in the cache for a longer time period than a slot having only a first cache hit. The cache may be organized as a plurality of memory banks of cache slots. Each memory bank has an associated control slot that includes groups of extents of tags. Each cache slot has a corresponding tag, and a time stamp. The time stamp of slots in the cache may be adjusted affecting the amount of time a particular portion of data remains in the cache.

Method for cache management for positioning cache slot

Storing data in a cache memory of a storage device includes providing access to a first segment of the cache memory on behalf of a first group of external host systems coupled to the storage device and providing access to a second segment of the cache memory on behalf of a second group of external host systems coupled to the storage device, where at least a portion of the second segment of the cache memory is not part of the first segment of the cache memory. In some embodiments, no portion of the second segment of the cache memory is part of the first segment. Storing data in a cache memory of a storage device may also include providing a first data structure in the first segment of the cache memory and providing a second data structure in the second segment of the cache memory, where accessing the first segment includes accessing the first data structure and accessing the second segment includes accessing the second data structure. The data structures may be doubly linked ring lists of blocks of data. Each block of data may correspond to a track on a disk drive. Different groups of external host systems may be provided with different access, priority, and level of service with respect to the different segments of the cache.

Segmenting cache to provide varying service levels

Storing data in a cache memory includes providing a first mechanism for allowing exclusive access to a first portion of the cache memory and providing a second mechanism for allowing exclusive access to a second portion of the cache memory, where exclusive access to the first portion is independent of exclusive access to the second portion. The first and second mechanisms may be software locks. Allowing exclusive access may also include providing a first data structure in the first portion of the cache memory and providing a second data structure in the second portion of the cache memory, where accessing the first portion includes accessing the first data structure and accessing the second portion includes accessing the second data structure. The data structures may doubly linked ring lists of blocks of data and the blocks may correspond to a track on a disk drive. The technique described herein may be generalized to any number of portions.

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Watertown, MA, United States of America

Daniel Lambright