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A technique to support large number of targets with efficient utilization of memory

IP.com Disclosure Number: IPCOM000198986D
Publication Date: 2010-Aug-19
Document File: 3 page(s) / 24K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method to allow a source cell to handle a large number of targets without consuming more cache memory than is required. The invention includes the development of two cell sizes, small and large, and a system for determining which size is needed to best support the number of targets.

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A technique to support large number of targets with efficient utilization of memory

Current flash copy design supports 12 targets. These targets are kept in cache

segments with the source cell. A cell has a fixed size to accommodate 12 targets. To

support more than 12 targets, for example 256 targets, a cell needs to be able to

accommodate 256 targets. One solution is to increase the size of the cell so that it can

keep a list of 256 targets. However, that means each cell consumes lot more space.

Since the majority of the flash copy sources will a small number of targets and only few

will have a large number of targets, this creates a waste of cache space.

A solution is required which allows a source cell to handle a large number of targets

without consuming more cache memory than is required for the present number of

targets.

Core idea of the invention is to have two cell sizes: one large(256) and one small(12).

When the number of relations increases so that the small cell has exceeded capacity,

then the system changes to the large cell. At that point, the system verifies whether the

new cell will fit in the current cache segment. If not, then it allocates a new cache

segment and splits the cells into the old and new cache segment. When the number of

relations decreases for a large cell such that the targets can now fit in a small cell, then

the system reduces the cell size. It also reviews the neighboring cache segments to

see whether it can merge the two segments; the system merges the two cache

segments where possible.

The following definitions apply to this invention:
• Relation/Relationship: relation is a logical copy of data from a source extent to a

target extent
• IMRE: In-Memory Relationship Entry or Relation Entry is a data structure that

describes a particular flash copy relationship
• IMRT: In-memory relation table. It contains information about all the relations for

a volume. The volume has a list of cache segments. Each cache segment has a

certain number of cells.
• PIMRE: Pointer to IMRE
• Cell: A cell contains all the relations for a...