Setting SCSI-adapter and disk-device queue limits
The operating system has the ability to enforce limits on the number of I/O requests that can be outstanding from the SCSI adapter to a given SCSI bus or disk drive. These limits are intended to exploit the hardware's ability to handle multiple requests while ensuring that the seek-optimization algorithms in the device drivers are able to operate effectively.
For non-IBM devices, it is sometimes appropriate to modify the default queue-limit values that have been chosen to handle the worst possible case. The following sections describe situations in which the defaults should be changed and the recommended new values.