Section 8.3. Backup of Raw Partitions

8.3. Backup of Raw Partitions

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 (although not always), when you refer to a raw partition, you are referring to 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 able to back 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 variants) or Master Boot Record (in Intel systems). This tells the system's firmware where to go to find the operating system kernel. This block of data normally can reside on the first slice, or root partition, of the operating system disk. In modern Linux systems, it resides in a special partition called /boot. It resides outside the "normal" filesystem and thus is not 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 is backed up. With a 100 MB root partition of an operating system, this is not a problem. If it's a multiterabyte raw device, it can fill up quite a lot of backup media very fast. Some products can intelligently read a raw partition and perform an incremental backup of its contents. It is a rare option as of the writing of this book, but it is worth investigation.