| 摘要 |
<p>A method for dispatching work requests in a data storage hierarchy in which directory data is promoted in variable length spans, the use of which are maximised even for work requests entering the work request queue after the span is chosen, is disclosed. A queue of work requests is initially scanned to determine if any requests therein require access to directory data stored in secondary storage within a prescribed proximity of that required by the next request to be dispatched. If such other work requests exist, then directory data in addition to that required by the next request to be dispatched is also promoted. To minimise seek time and rotational latency, the additional data is promoted from secondary storage in a single device I/O cycle. The additional data is chosen by adjusting the outer limits of the span as each work request in queue is scanned. After the actual promotion of the span of data, the existing work request is completed. Upon the ensuing scan of the queue the dispatch of any work requests stored therein and requiring access to data previously promoted is next completed. The additionally promoted data, known to be required by other work requests in the queue, is thus certain to be accessed before subsequent migration. The priority completed requests include those requests added to the queue after the span of data was promoted. Thus, the number of device accesses is further reduced by priority completing those requests entering the queue which by coincidence also require access to the additionally promoted data.</p> |
