Importance

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Abstract

A method and apparatus that transfers data between system memory which is arranged in pages and an attached storage system. In such a paged memory, data which crosses pages having contiguous virtual addresses may map to data which crosses discontiguous physical pages. Scatter-gather is advantageously employed in such a system in order to achieve the transfer data directly between, memory and storage usually by Direct Memory Access (DMA). A secondary storage device which supports scatter-gather usually includes hardware which will perform the necessary calculations to transfer the data to and from the correct locations in physical memory. The technique of the present invention is useful with storage systems that do not support scatter-gather and comprises determining for each data transfer the identity of any requested sector which lies completely within a physical page and the identity of any sector which crosses boundaries between discontiguous physical pages; and for those sectors which lie within a physical page, transferring the sectors directly between secondary storage and memory by DMA; and for those sectors which cross said boundaries, transferring each sector to either the memory or secondary storage via an intermediate buffer.

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First Claim