Recovering OSVault Archived Files Directly From Tape

There are several situations that can occur that will require you to recover files directly from a piece of magnetic tape, rather than through the disk cache.  These include:
- Loss of the disk cache and related database due to catastrophic failure such as fire or damage
- Export and movement of tape cartridge(s) to another location and desire to import those tapes
- Recovery of previous versions of files that may have been overwritten after initial migration

This post will cover the methods to accomplish the last situation: scanning a tape and recovering all the files on that tape that may have been overwritten later.

Recovering Old Versions Of A File
Recovering an old version of a file can be the most tedious process if you do not know exactly when that version was overwritten.  OSVault keeps a history of the last time that a tape cartridge was mounted, so that information can help to reduce the number of tapes that must be scanned to find an old file.
To scan a tape and recover all the files on that tape back to disk, you use the "tape_dump" CLI command.  There are two ways to recover files from that tape, either as "stubs" or as whole files.  There are different reasons to use each option.  A "stub" recovery, using the "-s" option to "tape_dump", will create a stub file in the OSVault maintained file system but will not read in all the data portion of that file until that file stub is read later.  This allows you to import an entire tape while only using a small amount of disk storage.  Then you can browse the files recovered, and copy/use only the file(s) desired, while not reading all the other undesired files into  disk storage.
You can also recover all files directly from a tape onto disk storage.  This would be used if you are reading a tape into a non-OSVault file system or if you know you need all files stored on a particular tape.  Keep in mind that LTO-5 tapes can have 1.5TBytes of more of files on them.
If you are on an OSVault system, you can use the "-v" option to the "tape_dump" command to have the robotics load the select tape cartridge volume into an unused drive for recovery.  Other operations can be active on the OSVault system at the same tape, such as migration and staging.  So, if you wish to recover the stubs of all files on tape A0000325L5 to an OSVault cache directory called "/cache/recovered_files", you would use the CLI command;
    tape_dump -v A0000325L5 -s -f /cache/recovered_files
This will cause the tape to load into a drive, when a drive is available, and to scan the tape and create a stub in the directly /cache/recovered_files for every file it finds on the tape.  After the tape_dump completes, or is killed with a control-c, the files can be displayed with either the web browser, file browser or command line, and the desired file can be retrieved by copying or reading the file.  That reading/copying of the file will reload the tape in the drive and initiate a staging operation, bringing all the data portion of the file back into disk cache.