short: the capacity of a used tape can be increased only by reformatting the tape medium.
This topic describes methods the IBM Spectrum Archive™ uses to modify data as if it were overwritten or erased.
LTFS does not overwrite data recorded on a tape medium, even if a file in the tape medium appears to be overwritten. Instead, LTFS does the following:
- Appends new data to the end of existing data in a data partition
- Modifies the index data so that the file entry included in the index points to the new data
The old data remains on the tape medium, but is no longer indexed by LTFS.
Note Older generations of the XML schema still reference the original data. On Linux and OS X systems, using the ltfsck command enables a rollback to older generations and gives the user access to that data. Refer to the topic Checking media using the ltfsck command in the Related information section. On a Windows system, rolling back is done by using the Rollback panel. Refer to the topic Rolling back media in the Related information section.
Similarly, LTFS does not erase data from the tape medium, even if a file in the tape medium appears to be erased. Instead, it removes only the file entry from the index. This means that even if the user removes the file entry from the index, the remaining capacity on the tape medium does not increase. Because data cannot be erased, the capacity of a used tape can be increased only by reformatting the tape medium. On Linux and OS X systems, reformatting is done by using the mkltfs command. Refer to the topic Formatting media using the mkltfs command in the Related information section. On a Windows system, reformatting is done by using the Format Medium panel. Refer to the topic Formatting media in the Related information section.
Attention Although a medium can be reformatted by using the mkltfs command in Linux and OS X, and the Format Medium panel in Windows, most data is not overwritten. LTFS does not have the tools to provide a secure erasure.