Tapes

Review this topic for more information on tapes.

Pseudo Tape Devices

Since pseudo tape devices are UNIX file names, specifying a separate UNIX file as a device provides the ability to read and write data to it at a high speed. Such uses can be:

A copy of the ABS disks in a pseudo tape for fast reloading.
High-speed file-save backups to a UNIX file.
A serial device or network link for transmitting data to some other destination.

NOTE	The underscore character is a reserved character and is not valid in a pseudo tape device name.

Pseudo tape devices do not need to be compressed. For compressed pseudo tape devices, data is written compressed and read uncompressed using gzip utilities (to eliminate the 2 GB file size limitation on compressed tape devices). At user specified limits (before compression), the UNIX file name changes and cascades the pseudo tape device to the new file name.

For example, given this tape definition in the pick0 configuration file:

tape /tmp/pseudo 10000 p lx # compressed tape

If a data save has more data than the limit specified (10,000 1024 byte blocks, on 10 MB), the device /tmp/pseudo is closed and the save cascades to /tmp/pseudo-1. After the second 10 MB is written, the device /tmp/pseudo-1 is closed and the save cascades to /tmp/pseudo-2. This process continues until the save is finished.

NOTE	There must be space in the UNIX file system, /tmp in this example, to store these compressed files.

Changing the Compression Method

Use the !SwitchZip.sh program to change your compression method (either Compress or Gzip).

Navigate to the /usr/lib/pick directory. For example:

cd /usr/lib/pick

Run the SwitchZip.sh program. For example:

!SwitchZip.sh

The Choose compression method menu displays.

Select your compression method and press ENTER.

The compression method is changed.

SCSI Tapes

SCSI tapes in D3 Linux all share the same naming convention regardless of type. Names prefixed with n refer to the non-rewinding version of the device, which will be used in D3 Linux. Device names use the format:

/dev/nstN

where N is a number. The mapping between the number and the actual tape drive depends on the SCSI ID and the SCSI controller used.

Multireel Saves

By default, D3 Linux does not support multireel saves. However, it can be configured to support multireel saves. If there is no intention to ever use multireel saves, do not enable this feature. Enabling multireel saves produces more wear on the tape. Multireel tape processing takes considerably longer than single-reel processing.

NOTE	The user must have root privileges and the D3 port must be started by entering d3 -0 -l (lowercase L).

To enable multireel saves:

Insert the media into the drive.
Execute these commands from line 0 (the console) at TCL, where device.name is the UNIX device name listed in the TCL command:

!mt -f device.name drvbuffer 0

!mt -f device.name stoptions 4

list-device

This disables the internal buffers, ensuring reliable end-of-media detection. As such, it may reduce tape streaming.

To restore the original state of tape operations:

Insert the media into the drive.
Execute these commands from line 0 (the console) at TCL, where device.name is the UNIX device name listed in the TCL command:

!mt -f device.name drvbuffer 1

!mt -f device.name stoptions 7

list-device

This re-enables drive buffering to assist streaming and reduce tape drive wear, but prevents reliable end-of-media detection.

4mm and 8mm Tape

To ensure proper operation of 4mm and 8mm tape devices, the block size of the drive must be set to variable block size mode. The variable block size mode setting is zero (0). After first setting the block size to the variable zero (0), you can change it to any size you choose.

However, when you change the block size to anything other than the variable zero (0), that change becomes the default block size for all other tape drives on the system.

NOTE	It is highly recommended that the default block size always be set to variable block size mode (0) because you can only perform a file restore when the block size is set to 0. In order to restore multireel tape saves, the block size should be set to variable block size mode (0).

Setting the Default Block Size for the Tape Drive

To use these methods you must ensure that there is not a tape in the drive.

NOTE	The user must have root privileges and the D3 port must be started by entering d3 -0 -l (lowercase L).

There are three methods available to set the block size for a tape that is not in the tape drive.

Method 1

Execute this command from the TCL prompt (or place the command in the dm,md, user-coldstart item (to ensure that the command is executed at system start up) by typing:

set-def-tape-blk block.size tape.number

For example, the tape device number is 5 and the physical block size is 0.

set-def-tape-blk 0 5

Choosing 0 sets the physical block size to a variable value. If you want to set the physical block size to a specific numeric value you can. In this instance, replace the variable value (0) with a numeric value.

For example, the variable block size 0 in the first example is replaced by the numeric value 512.

set-def-tape-blk 512 5

Method 2

Execute these commands from the TCL prompt by typing:

set-device tape.number

set-def-tape-blk block.size

Method 3

The last way to set a numeric value to a block size is to execute this command from the TCL prompt by typing:

!mt -f device.name defblksize block.size

Setting Block Size of a Tape Already in the Tape Drive

Ensure that there is a tape in the drive.

There are three methods available to set the block size for a tape that is already in the tape drive:

Method 1

Execute these commands from the TCL prompt by typing:

list-device

set-tape-blk block.size tape.number

Method 2

Execute these commands from the TCL prompt by typing:

set-device tape.number

set-tape-blk block.size

If you do not designate a tape number in step one, the block size will be set for the tape device to which the Rocket user is currently attached.

Method 3

Execute this command from the TCL prompt by typing:

!mt -f device.name setblk block.size