Fixed Media Drives
A fixed media drive refers to the use of hard drives as backup devices, although it can also refer to drive arrays containing multiple hard drives. Fixed media drives offer significant speed improvements over tape as a backup medium. Also, because they are recognized directly by the operating system, they are companionable with all backup software—including homemade solutions (such as backup scripts) or manual copying of files.
It is common to create RAID arrays when using fixed media for backup. A RAID array is a set of multiple physical hard drives tied together to behave as a single drive. RAID arrays come in various types and levels and can be used to increase performance as well as redundancy. The simplest RAID array, known as a mirrored array, ties two hard drives together as mirrors of each other. Each file copied to the drive as it appears to the computer is actually copied to both physical hard drives, providing redundancy if one drive fails. Other options include creating striped arrays (in which multiple drives each contain only a piece of the file for faster drive performance) and striped arrays with parity (which stripe data across multiple drives, but include parity information that can be used to regenerate lost data if a single drive fails).
Using a mirrored or striped with parity RAID array, you can easily create redundant backup drives. If one physical drive fails, the backup is still available (either in direct form on the mirrored drive or in a form that can be reconstructed). Thus, there are significant advantages in reliability over tape backups. Even without using an array structure, hard drives are generally far less fragile than tapes and don’t carry any special concerns about handling or storage.
Typically, when using fixed media drives (particularly in the case of a drive array), you will connect them directly to the servers that they will be backing up. Although this removes much concern about physically storing them, it does limit their use as an offsite backup option.
If you want to use fixed media drives for off-site backup devices, particularly for small organizations, you might be tempted to consider some of the smaller portable hard drives on the market. Several firewire drives can be powered directly from the firewire bus and have little additional bulk or weight over tape drives. You might want to consider these drives as your primary backup drive or as supplemental drives to provide offsite options, perhaps making offsite backups on a less frequent basis. The downside of this approach is that it might prove more difficult to integrate in an automated backup approach than other options.