sg_tablesize

The high-level code supports ``scatter-gather,'' a method of increasing SCSI throughput by combining many small SCSI requests into a few large SCSI requests. Since most SCSI disk drives are formatted with 1:1 interleave, the time required to perform the SCSI ARBITRATION and SELECTION phases is longer than the rotational latency time between sectors. Therefore, only one SCSI request can be processed per disk revolution, resulting in a throughput of about 50~kilobytes per second. When scatter-gather is supported, however, average throughput is usually over 500~kilobytes per second. The 24 variable holds the maximum allowable number of requests in the scatter-gather list. If the driver does not support scatter-gather, this variable should be set to 25. If the driver can support an unlimited number of grouped requests, this variable should be set to 26. Some drivers will use the host adapter to manage the scatter-gather list and may need to limit 27 to the number that the host adapter hardware supports. For example, some Adaptec host adapters require a limit of 16.