HP Surestore 28/48-Slot with DLT7000 Digital Linear Tape SCSI-2 Drive and SCSI - Page 276

Programmer's Tips Performance Tuning Data Transfer Size The tape drive transfers read and write data to and from the initiator in bursts based on the Maximum Burst Size in the Disconnect-Reconnect Mode Page 02H. This parameter controls how often the drive disconnects, reselecting the initiator during large data transfers. The default value for the Maximum Burst Size is 64 Kbytes. If the Maximum Burst Size is smaller, the target transfers data to and from the initiator while reading or writing data to the media. Each time the tape drive disconnects, the overhead for disconnect and reselect operations consumes additional SCSI bus time. To maximize performance, weigh these two factors: • The simultaneous data transfer with media operations • The overhead of the disconnect and reselect process Non-Volatile Configuration Values Configuration information is retained in the tape drive's EEPROM storage. Configure the values that maximize performance after a cache reset condition by using the Mode Select command. In many cases, the performance tuning parameters that yield the best performance varies between applications. To update the current operating parameters, the user may also include the Mode Select operation when invoking the application. Error Analysis The data returned in response to the Request Sense command has ten bytes of vendor information appended to the ANSI standard data. This information is helpful in analyzing the drive usage. Set the Allocation Length field in the Command Descriptor Block to a value greater than or equal to 28 for the tape drive and 78 for the autochanger to ensure that additional error information is available for analysis by the integrator and/or the tape drive development team. B- 6 Appendix B