Many environments use their commercial backup product to back up raw partitions. A partition is a section of disk that may or may not contain a filesystem. Typically, when one refers to a raw partition, it is a section of disk that does not contain a filesystem. This disk may contain data for a database product, such as Oracle, Informix, or Sybase. It also may be the first part of the root partition of the operating system disk that contains the boot block. Since most backup products are designed to back up files that reside on a filesystem, they may not be able to back up a raw partition.

The ability to back up raw partitions could help when backing up relatively small databases that reside on raw partitions. To back up most databases with a product that supports raw partitions, simply shut down the database and tell the backup software what raw partitions to back up. In order to do this, the backup software needs to be capable of backing up these raw partitions.

The second reason to consider the use of this feature is to back up the root partition of an operating system disk. It’s another way to recover the root disk without reinstalling the operating system. There are two essential parts to the operating system disk. The first is the operating system itself, which resides on one or more filesystems on that disk. The second is the boot block (in Unix) or Master Boot Record (in DOS relatives). This tells the system’s firmware where to go to find the operating system kernel. This block of data normally resides on the first slice, or root partition, of the operating system disk. It resides outside the filesystem and thus would not be backed up by normal procedures. If the backup product is able to back up the raw partition on which it resides, it’s possible to recover it without reinstalling the operating system. (This is covered in detail in Part IV of this book.)

Many of the popular backup packages now work with raw partitions. There is one drawback to backing up raw partitions, though. A raw partition is seen as one big file. That means that every time it is backed up, the entire partition will be backed up. With a 100-MB root partition of an operating system, this is not a problem. If it’s a multigigabyte raw device, it can fill up quite a lot of backup media very fast. There are products that can intelligently read a raw partition and perform an incremental backup of its contents. This is a new option as of the writing of this book, but it is worth investigation.