Tapes

Review this topic for more information on tapes.

Some differences in tape handling occur due to the way AIX drivers work. This section lists these differences.

Compatibility

There are some differences from what a D3 user might expect in the way tape is handled on AIX, due to the way the AIX drivers work. This section lists these differences.

Quarter-Inch Tape Compatibility

In the table below:

6157-001 is the 60 Megabyte IBM RT tape.
6157-002 is the 120 Megabyte IBM RT tape.
7207-001 is the multidensity RISC System/6000 tape.

Written by	Read by	3M Tape used	Compatibility
6157-001	7207-001	DC 300 XL/P	7207-001 will read tape
6157-001	7207-001	DC 600 A	Results are unpredictable
6157-001	7207-001	DC 6150	Results are unpredictable
6157-002	7207-001	DC 300 XL/P	6157-002 cannot write
6157-002	7207-001	DC 600 A	7207-001 will read tape
6157-002	7207-001	DC 6150	7207-001 will read tape
7207-001	7207-001	DC 300 XL/P	6157-002 cannot read or write
7207-001	7207-001	DC 600 A	7207-001 will read and write
7207-001	7207-001	DC 6150	7207-001 will read and write

NOTE

Not all possibilities are covered in this chart.
DC 6150 is the new name for the 3M DC 600 XTD.
DC 300 XL/P is designed for the 6157-002; the DC 600 A and DC 6150 are designed for the 6157-002; the DC 6150 is preferred for the 7207-001.
Generally, a high-density drive can read a low density tape, but cannot write to it.

Tape Device Differences

Floppy

When removing the floppy disk from the drive, the device light must be off and the floppy must be detached (unloaded). Otherwise, the system reports parity errors. This is not the case in multiple floppy save/restore.

t-rew or set-floppy does not actually access the drive. Therefore, the diskette drive light does not go on, but it does work properly.

Quarter-Inch Tape

After a file-save or after the last t-dump on a tape, always do a t-rew or t-unld to ensure that a second file mark is written to the tape, making a logical end-of-tape marker. Without this precaution, only one file mark is written at the end of the tape. This might cause problems when restoring the tape on some non-D3 systems, or will cause the system to prompt for an additional, nonexistent reel when doing a selective restore or an account restore from a tape on which the account is not saved. Even without doing the t-rew or t-unld, a restore from the tape will work properly.

Detaching the tape may force a rewind.

t-rew waits until the tape is rewound, instead of returning immediately to TCL.

If a sel-restore or account-restore on a full file-save tape was made on an older version of AP or a non-AP system, and that tape does not contain the specified account, the system asks for one more than the actual number of reels. If this creates a problem, use the (f option to force reading all files.

After a file-save or after the last t-dump on tape, a dummy label is added after the two file marks by the t-rew or t-unld. Since this block is beyond the logical end of tape, it should not create a problem. However, if the tape is read using readt in FlashBASIC, and if the double file mark is ignored by the program, this block becomes visible.

Half-Inch Tape

Executing a t-det can force a rewind.

t-rew waits until the tape is rewound before returning to TCL.

t-unld executes a rewind only. The tape has to be unloaded manually. This is also the case when changing reels on a multireel save or restore.

On the IBM tape drive, only two densities are supported:

1600 bpi (rmtX.5)
6250 bpi (rmtX.1)

On the Cipher tape drive with the appropriate Dickens Data Systems Driver and Cipher SCSI interface CSC100, three densities are available:

1600 bpi (rmtX.1)
3200 bpi (rmtX.3)
6250 bpi on the model 990 (rmtX.5)

NOTE	The densities are coded differently for the IBM and Cipher tape drives.

Video/8mm Tape

Some D3 Licensees write the D3 label inside an 80 byte block, while D3 expects the label to be written at the beginning or at the end of a 512 byte block. When trying to read this kind of tape, tape format errors occur because the label is not understood and some data is rejected by the tape handler. To resolve this problem, and to write 80 byte label blocks, use the chg-device command. See the D3 Reference Manual for more information. Remember to set the 512 byte block format after using the tape; if a file-save is done with an 80 byte label, it is not possible to do a full file restore from this tape.

NOTE	The restrictions for the SCT apply to the 8mm tape as well.

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.