The First Line of Defense

Backup and restore is the cornerstone of data protection. Because the earliest computer systems began to collect and manipulate data, having an extra copy of the data for later retrieval has been the most common method of protecting against data loss.

Figure 3-0.

Backup simply means making copies of data to a different device from the original one, for purposes of restoring it later. The difference between backups and copies made for other purposes is the goal. Whereas other copies of data are made to transfer information or provide for failover, backup data is not meant to be immediately available. The data on the backup media cannot be used in place of the primary system while it is down. Instead, it must be restored to the original or a replacement system, using a process called restore. Backup is useless without restore, and restore can't happen without a good backup.

There are many ways to back up data. In some instances, making a copy on a floppy drive is sufficient. That works well for individuals but not for an enterprise of any size. The classic backup media is magnetic tape. Until recently, tape was almost synonymous with backup. All backup and recovery software was designed to work with tape. So prevalent is tape that newer disk-based systems often try to emulate tape backup for compatibility reasons.

For many years, backup and recovery were dull backwaters. Although backup represented a point of pain for IT departments, most of the energy of the data storage industry was focused on making tape systems work better. Tape drives have gotten faster, and media can hold more data than ever before. SAN architectures allow for faster backup of more computers. Very little that was fundamental to backup changed until the late 1990s. At that point, tape was no longer able to keep up with the demands of many businesses. Since then, new ways of supporting backup and recovery operations have been devised.

Now the system architect can choose among many different methodologies and technologies when designing a backup system. Although this makes for more efficient backup and recovery operations, it also complicates design and implementation. It is worth the effort, though. The demands that businesses place on the backup process are increasing and will continue to do so as corporate information becomes more and more valuable.

The Backup Window

Performing backups during heavy system usage times creates problems. Application data may be locked when the backup software needs to copy them. The backup software might do the same, causing applications to fail. Backups tend to create heavy system loads, which slow servers and cause network congestion. All of these cause adverse effects on the system response time and annoy end-users immensely.

For these reasons, backups are usually run when the system load is the lowest, to prevent slow system response times and application timeouts. Typically, this means that backup is done in the middle of the night. The interval when backups can be performed without affecting other systems is called the backup window.