Online Backup Services and Data Retention

The primary reason that most people backup their data is to protect against a catastrophic loss such as a hard disk failure. There are some other important reasons for backing up data that are just as critical. A well thought-out data backup strategy can protect against losses other than catastrophic or sudden losses. There are several factors that determine the usefulness of backup data to recover from various losses. Frequency of backup, storage location, type of backup (full, incremental, or differential), and retention policies are all relevant factors when backup data is needed to recover from a loss.

An entire class of data loss involves data corruption, errant modifications, and deletions that aren't detected immediately. I call these latent data losses because there is a latency between the time the data was lost and the time the loss becomes known. Note, the term "data loss" refers to any loss or undesired modification of data. Latent data losses are usually not caused by a hardware failure. Some common causes are; human error, malicious code, or errant processing. These losses can be especially insidious because the problems can infect the data backup systems as well as the primary data. Suppose an accounting file is mistakenly deleted and the file is not discovered missing until the end of the quarter. Several daily backups may have run since the file was deleted. The current backup media does not contain the missing file, nor do any of the recent backups. There are numerous other events that can corrupt or destroy data that go undetected for days, weeks or months.

Public companies that operate in the United States are compelled by the Sarbanes-Oxley Act of 2002 to retain certain data for periods of 5 to 7 years. While failure to comply carries stiff penalties, most companies with competent management choose to retain data for more direct business reasons. The ability to access historical backup data is an important safety-net, offering macro-scale "undo" and "redo" capabilities for business processes. Even small businesses and individuals can benefit from the ability to undo a mistake that was made days or weeks earlier.

Online backup and disk-based backup systems have some distinct advantages over traditional removable media type backups when it comes to backup data retention. Online backup systems allow the flexibility to retain individual files rather than entire media sets. Most disk-based systems, including online backup, economize storage space by eliminating duplication of backup data. Once a file has been backed up, there is no need to make another exact copy of the same file for retention purposes as is often the case with tapes and other removable storage. There are also many situations where removable media storage will require that thousands of files are retained unnecessarily because a few files on the media need to be retained. Because of the high cost of tape media, many companies unnecessarily limit their backup data retention to control the cost of backup media.

I highly recommend using an online backup service, but many of the services don't provide any meaningful control over the retention of backup data. The free and cheap services restrict retention of deleted files and older versions of files to very short time periods, if any at all. Online backup services that don't allow control over retention only offer protection from the most basic data losses and offer no protection from latent data loss. By trying to save a few bucks by using the cheapest online backup service, you are seriously reducing the value of backing up your files. A number of good online backup services are relatively inexpensive and provide excellent protection from all types of data loss. A good professional online backup service will allow you to specify your own retention policies that meet your actual needs rather than forcing a retention policy on you that meets the needs of the online backup service provider.