Docker container for managing tape (lto) drives

Includes mt-st package which provides the mt command for interfacing with tape drives, as well as gnu tar.

Also includes cron for scheduling tape backups and restores. Crontab is included in the /config folder and changes require a container restart.

Requirements:

• Needs the tape devices mounted (ie. --device /dev/st0 --device /dev/nst0)
• Needs a bind mount for the /config folder
• Add optional bind mounts for the paths you'd like to copy from and to

Usage:

Basic facts about tapes and how they are operated with mt and tar:

• Tape drives are for sequential reading and writing. Each tar file is written and appended with an EOF marker that defines the end of the file.
• Tape drives can easily and relatively quickly identify the EOF files to determine the beginning and end of each file.
• Writing and reading operations always begin on where the drive head currently is. Pay close attention to that prior to each operation.
• /dev/st0 is a rewinding device. After each operation, the tape is rewound to the beginning. /dev/nst0 is non-rewinding and the head remains at its location at the end of each operation.
• mt -f /dev/nst0 status will show the status of the drive head. If it's at a file (vs a block), it will list the File number. If it's at the beginning of a file, it will list EOF at the bottom (except for the first file, which is really called File number=0, which will show BOT indicating the beginning of tape).
• You can seek to the beginning via mt -f /dev/nst0 rewind or mt -f /dev/nst0 asf 0
• You can seek to the beginning of any file via mt -f /dev/nst0 asf Xwith X being the file number (starting from 0)

Writing to tape:

• For the first write, make sure to rewind via mt -f /dev/nst0 rewind and confirm with status.
• With tar, you can write directly to the tape via tar -cvf /dev/nst0 sourcedirectory1 sourcedirectory2.
• If you used the non-rewinding nst0 device, the drive head should be at the beginning of the second file, indicated by File number=1 and EOF in status output.
• To write the second file, make sure the status shows File number=1 and EOF.
• Same command, tar -cvf /dev/nst0 sourcedirectory1 sourcedirectory2, will now write the second tar file and the head should move to File number=2.
• If you overwrite the first file, all subsequent files will be lost. Pay attention to where the head is before each write operation. You can use mt to forward to the end of the tape to be sure.
• For long operations run manually via cli, you can use screen so you don't have to keep a shell open.

Reading from tape:

• You can seek to the beginning of files with the command mt -f /dev/nst0 asf X with X being the file number (starting with 0).
• To copy the first file from tape to the current folder on the local machine, rewind via mt -f /dev/nst0 rewind (or via mt -f /dev/nst0 asf 0).
• Use the tar command to extract from tape: tar -xvf /dev/nst0. It will read the first file all the way to the EOF, and extract it to the local disk.
• To copy the second file from tape, seek to it via mt -f /dev/nst0 asf 1 and extract via tar -xvf /dev/nst0.
• For long operations run manually via cli, you can use screen so you don't have to keep a shell open.

There are plenty more mt commands and arguments listed on its manpage: https://linux.die.net/man/1/mt

Important Notice:

Never do mt -f /dev/nst0 erase unless you know it's really what you want. The manpage is not clear about it, but it actually does a secure erase, it takes a really long time (8+ hrs) and you can't cancel it once started. Killing or force killing the process doesn't work, docker stop and docker kill fail. The only way is to cut the power to the drive, which could damage the drive head.