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Archiving Sparse Files

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A file is sparse if it contains blocks of zeros whose existance is recorded, but that have no space allocated on disk. When you specify the `--sparse' (`-S') option in conjunction with the `--create' (`-c') operation, tar tests all files for sparseness while archiving. If tar finds a file to be sparse, it uses a sparse representation of the file in the archive.

FIXME: xref Creating Archives
, for more information about creating archives.

`--sparse' (`-S') is useful when archiving files, such as dbm files, likely to contain many nulls. This option dramatically decreases the amount of space needed to store such an archive.

Please Note: Always use `--sparse' (`-S') when performing file system backups, to avoid archiving the expanded forms of files stored sparsely in the system.

Even if your system has no no sparse files currently, some may be created in the future. If you use `--sparse' (`-S') while making file system backups as a matter of course, you can be assured the archive will always take no more space on the media than the files take on disk (otherwise, archiving a disk filled with sparse files might take hundreds of tapes).

FIXME: xref incremental when node name is set.

tar ignores the `--sparse' (`-S') option when reading an archive.

Files stored sparsely in the file system are represented sparsely in the archive. Use in conjunction with write operations.

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