Changeable parameters

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The configuration parameters are used to set the operating mode of the tape drive and device driver when a device is opened. The changeable parameters are detailed as follows.

Barcode length

This parameter can be set to change the barcode length for a cartridge. For LTO cartridges the default is 8. It can be changed to 6 for LTO 1 and LTO 2 generation cartridges only. For 3592 cartridges the default is set at 6. It can be changed to 8. In the /etc/modprobe.conf.local file the following line must be added to reflect the desired change.

options lin_tape ibm3592_barcode=8
options lin_tape lto_barcode=6

Block size

This parameter specifies the block size that is used for read and write operations. A value of zero means a variable block size. Any other value is a fixed block size. The installation default is zero (variable length block size). Refer to Maximum SCSI transfer length for guidance.

Buffered mode

This parameter specifies whether read and write operations must be buffered by the tape device. The default (recommended) value is TRUE.

Capacity scaling

This parameter sets the capacity or logical length of the current tape on Enterprise Tape System 3590 or 3592 tape subsystems. By reducing the capacity of the tape, the tape drive can access data faster at the expense of data capacity. Capacity scaling can be set at 100% for the entire tape (which is the default), or set at 75%, 50%, or 25% of the 3590 tape cartridge and more available capacity scaling for the 3592 standard 300 GB rewritable data cartridge. Capacity scaling remains with the tape across mounts until it is changed.

Note:

The tape position must be at the start of the tape to change this parameter from its current value.
Changing this parameter destroys any existing data on the tape.
For 3592 media types, capacity scaling is supported only for the standard 300 GB rewritable data cartridge. Attempting to set capacity scaling that is not supported by a device or the current loaded media always returns 100% and cannot be changed. For example, the 60 GB (Economy Data) cartridge for the IBM® 3592 cannot be capacity-scaled and is always 100%.

Compression

Hardware compression is implemented in the device hardware. This parameter turns the hardware compression feature On and Off. If compression is enabled, the effective performance can increase, based on the compressibility of the data.

The installation default is On (use compression).

Disable auto drive dump

This parameter is provided in the lin_tape version 1.2.2 or later. It is set to FALSE by default. If it is FALSE and the lin_taped daemon is running and if an error occurs in the drive that creates a drive dump, the lin_tape device driver automatically retrieves the drive dump and saves it under the /var/log directory by default. You can specify another directory in the /etc/lin_taped.conf file. The dump is labeled with a .dmp extension on the file. Refer to Configuring and running the lin_taped daemon for details.

Disable SIM logging

This parameter is provided in the lin_tape version 1.2.2 or later. It is set to FALSE by default. If it is FALSE and the lin_taped daemon is running and SIM/MIM data is generated by the drive, the lin_tape device driver automatically retrieves the data and saves it in a formatted text file under the /var/log directory by default. You can specify another directory in the /etc/lin_taped.conf file. Refer to Configuring and running the lin_taped daemon for details.

This capacity is not applicable to IBM Ultrium tape drives.

Dynamic attributes

This parameter determines whether dynamic runtime attributes are attempted on open for supported drives. Default is 1 (on) meaning that the driver automatically attempts to set dynamic runtime attributes on open. This parameter can be changed to 0 (off) in the configuration file before the lin_tape is loaded. It is recommended to keep on dynamic attributes unless it produces an unexpected problem in the environment.

Logging (volume logging)

This parameter turns the volume information logging 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 logging is On and the lin_taped daemon is running, the lin_tape device driver retrieves the full log sense data from the drive whenever a tape is unloaded, or the drive reaches a log threshold. The log file is saved in binary format under the directory /var/log by default. You can specify another directory in /etc/lin_taped.conf file. Refer to Configuring and running the lin_taped daemon for details.

Note: This parameter is volume logging, which is different from error logging. lin_tape provides error logging whenever the lin_taped daemon is running. Refer to Configuring and running the lin_taped daemon for details on error logging.

Logical write protect

This parameter sets or resets the logical write protect of the current tape on Enterprise Tape System 3590 tape subsystems. The three types of logical write protect are associated protect, persistent protect, and write-once read-many (WORM) protect.

Associated protect remains only while the current tape is mounted or associated with the tape drive. It is reset when the tape is unloaded or the tape drive is reset.
Persistent protect remains or persists with the tape across mounts until it is reset.
WORM protect also remains with the tape across mounts, but unlike persistent protect it cannot be reset on the tape. After a tape is WORM protected, it can never be written on again.

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 is 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 can increase the maximum transfer length to enhance the data throughput. This procedure can be done with ITDT with the Query/Set Parameters option, 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.

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 greater than 256 KB. It cannot be changed by the STIOCSETP ioctl call any more.

Read past filemark

If this parameter is set to true, when a fixed-length read operation encounters a filemark, it returns the number of bytes read before the filemark is encountered and positions the tape head after the filemark. If the read_past_filemark parameter is set to false, when the fixed-length 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 runs faster, but the next command takes a long time to finish unless the physical rewind operation is complete. 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 can specify another directory in /etc/lin_taped.conf file. Refer to Configuring and running the lin_taped daemon for details.

Trailer labels

If this parameter is set to On, then writing records past the early warning mark on the tape is allowed. The first write operation after detecting the early warning mark fails and the errno variable is set to ENOSPC. No data is written during the operation. All subsequent write operations are allowed to continue until the physical end of the volume is reached and errno EIO is returned.

If this parameter is set to Off, then writing records past the early warning mark is not allowed. Errno variable is set to ENOSPC.

The installation default is On (with trailer labels).

Busy Retry

The parameter busy_retry determines how many times to retry a command when the device is busy. Default is 0 (off), and can be set up to 480 in the configuration file before the lin_tape is loaded.

lin_tape_ignoreOEM

The parameter lin_tape_ignoreOEM stops OEM devices from connecting to the driver. Default is 0 (off), and can be set up to 1 in the configuration file before the lin_tape is loaded.