## Storage Device Driver Reference

[prev][next][parent][TOC]

### Sorting and Priority

Requests should be sorted into internal queues based on physical disk location and I/O priority to optimize request servicing. Lower priority requests should be satisfied only where they do not significantly slow service of higher priority requests (for example, when a lower priority request refers to a sector in the same cylinder as a high priority request) . Because the format of requests in Request Lists is different from the format of standard OS/2 requests, the queue management DevHlp routines cannot be used.

The queueing strategy adopted by the driver is highly dependent on the devices it services. In general, efficiency and request priority are the primary concerns in determining a queueing strategy. Lower priority requests should never slow service of higher priority requests. Lower priority requests can be serviced in the context of servicing higher priority requests, so long as no time-costly operations are necessary to service the lower priority requests. In addition, where contention for resources such as auxiliary, driver-allocated buffers or space on a controller buffer is an issue, higher priority requests should be given preference.