File: //usr/share/webmin/virtual-server/help/backup_compression.html
<header>Backup compression format</header>
This field allows the compression type to be overridden for this backup. If
not set, the global default format (set on the Virtualmin Configuration page)
will be used. <p>
By default, Virtualmin uses <tt>gzip</tt> compression on its backup files. However, this
option can be used to select the space efficient (but CPU-intensive) <tt>bzip2</tt>
format instead. You can also use un-compressed <tt>tar</tt> format backups, which may be
useful if you want a speedy backup, or if you are writing to tape. Or the
<tt>zip</tt> format, which is easier to extract on other operating systems. <p>
This option is only used when backing up virtual servers to a directory, with
one file per domain. When backing up to a single file, the filename determines
the compression format (like <tt>domains.tar.gz</tt> or <tt>domains.tar</tt>).
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