IBM TS2340 User Guide - Page 124

Linux Device Driver (lin_tape) Note: The tape position must be at the start of the tape to change this parameter from its current value. Maximum SCSI Transfer Length In the lin_tape drivers with level lower than 3.0.3, the maximum transfer length per device per SCSI command is 262144 bytes (256 KB) by default. Variable block read/write requests with transfer length greater than the maximum transfer length fails [errno: EINVAL]. When a fixed block size has been defined, large write requests are subject to both the granularity of the block size and the maximum transfer length. For example, with a fixed block size of 80000 bytes and maximum transfer length of 262144, a write request for 400000 bytes (5 blocks of 80000 each) is written to tape in two transfers. The first transfer is 240000 bytes (3 blocks) and the second transfer is 160000 (the remaining two blocks). You may increase the maximum transfer length to enhance the data throughput. This can be done either using IBMtapeutil, option 48 - Query/Set Tape Parameters, or a customized STIOCSETP input/output control (ioctl) call. However, setting the transfer length greater than the default 256 KB does not guarantee a noticeable increase in data throughput. Maximum transfer length of 256 KB is highly recommended. Note: This is performed using tape diagnostic and utility functions. In lin_tape driver with level 3.0.5 or higher and the open source driver lin_tape, the maximum transfer length is defined as the minimum length that the host bus adapter and the tape drive can support. This number is usually greater than 256KB. It can not be changed by the IBMtapeutil, option 48 or the STIOCSETP ioctl call any more. Read Past Filemark If this parameter is set to true, when a read operation encounters a filemark, it returns the number of bytes read before encountering the filemark and positions the tape head after the filemark. If the read_past_filemark parameter is set to false, when the read operation encounters a filemark, if data was read, the read function returns the number of bytes read, and positions the tape head before the filemark. If no data was read, then the read returns 0 bytes read and positions the tape head after the filemark. This installation default is FALSE. Rewind Immediate This parameter sets the immediate bit for rewind commands. If it is set to On, the rewind tape operation executes faster, but the next command takes a long time to finish unless the physical rewind operation has completed. Setting this parameter reduces the amount of time it takes to close a device for a Rewind on Close special file. The installation default is Off (no rewind immediate). Trace This parameter turns the trace facility On or Off. With the lin_tape version 1.2.2 and later, the lin_tape device driver provides this support. It is set to On by default. If trace is On and the lin_taped daemon is running, the lin_tape device driver retrieves the trace from the driver if trace level is set to 1 or 2 in the /etc/lin_taped.conf file. The trace file is saved under the directory /var/log by default. You may specify another directory in /etc/lin_taped.conf file. Please refer to "Configure and Run lin_taped Daemon" on page 116 for details. 106 IBM Tape Device Drivers Installation and User's Guide