Support of a Standard or Custom Backup Format
A custom backup format is one that is readable only by a particular commercial backup utility. Backups made in a custom backup format cannot be read by native backup utilities such as tar, cpio, or dump. Some backup products use a custom format that is published or freely available. Although their backups can’t be read with native utilities, a programmer theoretically could write a program that would read their backups. There are also some backup products that are completely proprietary. In fact, some products are so proprietary that even their own product can’t read a volume if the indexes for that volume have expired or been deleted. A standard backup format would be a format that is readable by a standard utility. There are two schools of thought on this subject.
There are those who feel that using proprietary or custom backup formats is dangerous. If the backup volumes can’t be read by native utilities, then what do you do when the commercial backup product is broken? They prefer to use utilities that back up using industry standard backup formats such as cpio or tar.  They provide a sense of security that is just not possible when using a unique backup format. Companies often switch backup products, and when that happens, their old volumes are not readable by the new product. If the volumes were readable by standard utilities, however, they still could be used for restores.
There are several vendors on both sides of ...