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Beyond Basic Backups

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Beyond Basic Backups

Several new approaches have been developed in recent years to improve data security and reliability, but the discussion here covers only two of the more widely used ones: data mirroring and offsite backups.

Mirroring

Doing a backup involves taking a snapshot of the entire system at a given point in time and saving a copy of it, but mirroring is a more dynamic process. Every time a user changes a file, that data is recorded in more than one location — a process known as mirroring. That way, even if one set of the data goes down, the other set is available online. This can save a lot of time, because with a regular backup that data would be unavailable until it had been fully restored. Mirroring also has the advantage of being more current than backup because the data is constantly updated, whereas backups are usually done just once a day. The flip side, however, is that this benefit can sometimes turn into a liability. If a file becomes corrupted or is deleted, for example, it is no longer available at either location; therefore, the smart thing to do is to use traditional backups as well as mirroring to ensure data integrity and recoverability. The simplest way to achieve this is to have the data recorded in two partitions on the same disk. This system protects against the file being recorded in a bad sector but is of very limited value beyond that.

A step up is RAID-1, where two disks, run by the same controller, each record the data. This provides greater data protection than mirroring onto a single disk, but if the controller goes down, the data is lost. Disk duplexing provides even greater reliability by storing the data on two disks within the same system, but each with its own controller. Clustering, Network Attached Storage, or Storage Area Networks can also be used to provide redundancy.

Offsite Replication

Each of these approaches protects against a particular device failing but not against the data center going down. With remote mirroring, however, the data gets replicated to servers at another facility. The most famous recent example of remote mirroring occurred when a number of companies were able to operate despite their offices being destroyed in the World Trade Center attacks because their data centers were protected.

Among the several approaches to offsite storage, a company can simply purchase software such as LifeKeeper from SteelEye Technology, Inc. (Mountain View, California) or SnapMirror from Network Appliance, Inc. (Sunnyvale, California) to mirror files between their offices. The data can be updated on a moment-to-moment basis or synchronized on a set time interval. An alternative to running remote sites on one's own is to use a storage service provider (SSP). LiveVault Corporation (Marlborough, Massachusetts), for example, first performs a full backup of its customers' systems and then continually backs up changes as they occur. The data is stored at secure facilities managed by records storage firm Iron Mountain, Inc. The service works with Windows NT/2000 servers and requires a persistent connection of at least 128 kilobits per second (kbps). Clients who need to restore files can access the LiveVault backups via a browser and download the necessary files, or LiveVault will send the files on CD-ROM via an overnight delivery service.

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Backup Cautions

With the array of tools and solutions now available, data can be backed up and restored with greater ease and reliability than ever before, but a couple of important warnings should be kept in mind. The first is that backup is a secondary, not a primary, security solution. Having to rely on a backup is an admission of failure. It does not replace tools that monitor the health of disk drives or other device components that can predict and prevent disk failure, nor does it eliminate the need for an undelete utility. While the big disasters attract all the attention, 90 percent of the time the files that need to be restored were accidentally deleted by users. Using an undelete utility is much simpler and quicker than restoring a file from a backup tape.

Another important point: The result you are looking for is not just a quick and easy backup, but a complete and accurate restore; therefore, a test restoration of data should be performed regularly, at least once a month. One company I worked for, for example, had dutifully made backup tapes for years . But, as the tape drive grew older, its drive belt started slipping which caused the tape to move at uneven speeds. It was not a problem to record the data, but later, when files had to be restored, the tapes would no longer synchronize. It is unlikely that such a situation will happen again, but always be sure that you will be able to get your data back when you need it.

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