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All about Backups

Common wisdom holds that backing up files on personal and business computers is essential, yet this crucial task is often ignored. The only way to ensure timely and reliable backups is to devise a clear strategy and stick to it. We'll help you consider all aspects of your backup strategy, so you can make informed decisions. But simplicity is our watchword, because you probably won't back up if the process is too complex.

Why back up?

Like the manuscript for your great novel, some files are simply irreplaceable. Regular backups ensure you don't lose such files. But most files could be recreated given an unlimited budget for time and effort. Consider just how much time, money, and effort it would take to recover a system whose files were destroyed by mechanical failure, a virus attack, or user error. Also consider how much money you would lose simply because of downtime. A major purpose of backing up is to avoid such expenses. This is important to remember, since a strategy that costs too much time or money to implement may be counterproductive.

What to back up.

In the dark ages of computing, a "large" hard drive held 10MB, and floppy disks were the only option for backup media. Then it made sense to back up only the most essential data files. But with today's immense drives, reinstalling a modern operating system is quite a job, not to mention reinstalling and configuring dozens of applications. Even if you wanted to back up only data files, they may not all be in one handy location. Perhaps your computer is used only for Web research and e-mail. You'd still find it frustrating to lose all your bookmarks, cookies, settings, and e-mail addresses. Configuration settings for your applications are scattered in proprietary files, INI files, and the Registry. The simplest strategy is to back up everything, and simplicity is essential.

How to back up.

traditional backup has involved copying data to removable media such as disks, tapes, or CD-Rs. If you're backing up 20GB of data onto a 5GB-capacity tape drive, however, you've got a problem: Somebody must hang around and feed in new tapes as needed. That's not easy, and when backup isn't easy it doesn't happen.
If you opt for removable media, choose a type that's large enough to hold one entire backup. That probably means tape, since modern tapes can hold 60GB or more. Tape autoloaders automate the process of backing up to multiple tapes, but they're quite expensive. When using removable media, you can save space by using differential or incremental backups.
You can also back up a precise image of an entire drive's contents by using a product such as Symantec Ghost, or PowerQuest's Drive Image 2002 When you restore a drive image—whether to the same drive or a different one—the contents remain precisely as they were when the image was made.
You might think the image file would be as large as the drive's entire capacity. Fortunately, the file is compressed, and unused disk space is not stored, but the files can still be quite large. Depending on the file size, you can copy the image to CD-R, to another drive, or to a server on the network.
Many sites offer to back up your data on the Internet. One example is Connected TLM. Typically users are charged a fixed subscription fee per month for a specific amount of storage. The initial upload can be daunting, and you'll want to find a solution that lets you split the process into multiple sessions. Thereafter, only changes are uploaded, so the process goes much faster, but a broadband connection is a must. The amount of storage provided may not be enough for a full backup of all files, and you can't necessarily restore operating-system files. (Internet backup is really intended for data files.) Also, you generally don't have the option to store multiple backup sets, so if a backed-up file is corrupted, it may not be recoverable. Internet backup can be a good second line of defence for your most essential data files

When to back up

You should back up your data every day that you work on your computer. A business that's open on weekdays should back up at the end of each weekday, for example. If a virus wipes out data on a Wednesday, you can restore Tuesday's backup and lose no more than a day's work. But what if the backup files are also infected? What if the virus actually entered the system last month? A backup strategy with depth will also retain older backups at specified intervals. Backup administrators have devised strategies that rotate backup sets on a schedule that provides depth while balancing other needs. All but the simplest rotation strategies require the attention of a dedicated backup administrator. If you back up using drive imaging, the limiting factor is not the cost of removable media but the availability of disk space. The same rotation strategies can apply, but instead of reusing a tape, you simply delete the corresponding old image.
Some backup systems can operate in the background while the computer is in use. Others must run at the end of the day, when regular work has ceased. Some drive-imaging solutions actually require the computer to restart in order to back up. You'll need to consider these time factors when devising your strategy.

Where to keep backups

If removable-media backups are stacked next to the computer, a fire or other disaster will probably destroy both. A secure off-site location is best. At the very least, you should securely store them as far from your computer as possible. With the rotation strategies described below, consider keeping only the daily tapes in the office and storing all others off-site.
If your backup is an image file on another drive in the same computer, a virus could wipe out both. The best location for image backups is a high-capacity server on your network, preferably in another office, or at least a drive on another computer.
Internet backup is about as off-site as you can get, but the data is completely out of your reach. Although it's unlikely, the backup company could lose your data or go out of business. If you rely on Internet backup, consider using more than one site just in case.

Who should do the backup

In an ideal world, nobody would back up, because the process would be completely automated. Your backup strategy should hew to this ideal, automating the process as much as possible. In a small business, assign a backup administrator to be in charge of the entire process. If you must rely on individual users, make the process as painless as possible. For removable-media backups, make sure an entire backup fits on a single tape or other medium. The simpler the process and the fewer people involved, the better your chances for full recovery.

Differential and Incremental Backups

Most files don't change from day to day, so you can save time and money by backing up only the ones that do change. The file system keeps track of modified files using the archive bit. Any time a file is created or modified, the file system sets the archive bit to 1. Backup software clears the bit (that is, sets it to 0) for each backed-up file. You can see the status of the archive bit for any file by right-clicking the filename in Explorer, choosing Properties, and finding the Archive check box near the bottom. There are three types of backup that use the archive bit: full, differential and incremental

• A full backup, as its name implies, copies everything on the hard drive and clears the archive bit for every backed-up file. Restoring from a full backup is a one-step process, but the backup may be quite large.
• A differential backup copies only files that have changed since the last full backup and does not change the archive bit for those files. To restore using a differential backup, you must first restore the most recent full backup, followed by the most recent differential backup.
• An incremental backup copies files that have changed since the last full or incremental backup and clears the archive bit for all files copied. To restore, you must first restore the last full backup and then restore every incremental backup since that time, in order.

Using differential or incremental backups reduces the amount of storage required but increases the complexity of the process. One simple strategy is to make a full backup at the end of each week and a differential or incremental backup at the end of each day. Never mix incremental and differential backups!
The archive bit has been around since the early days of DOS, and it's not a wholly reliable indicator of changed files. Any program can change it with a simple Windows function call, and any user can reset it using the Properties dialog. Also, files that were deleted between the last full backup and the latest incremental/differential backup will reappear if you must restore.
Until recently, a drive-image backup was by definition a full backup, but the latest version of Symantec Ghost includes incremental backup. You can store a full backup and append incremental images that represent only the changes.

Rotation Strategies for Removable Media

Because your most recent backup may be corrupted, you'll want to keep older backups at varying intervals. But tapes or other media can get expensive, so the rotation scheme shouldn't use more of them than necessary. And because tapes wear out eventually, they should be used as evenly as possible. Backup administrators have devised various strategies for balancing these needs, some more complex than others. For maximum protection, these schemes assume full backups, done each workday. (For simplicity, we'll call all removable media tapes in this discussion.)

The simplest rotation strategy is called father/son (table 1). A weekly father/son scheme backs up each day's work on that day's tape, alternating between two different tapes for Friday. This scheme uses just six tapes and has a depth of up to two weeks. One variation uses two tapes for each day of the week and alternates between the two sets.

The grandfather/father/son (Table 2) strategy extends the father/son strategy for greater depth. For Monday through Thursday, you simply back up to that day's tape. On three of the four Fridays each month, you back up to one of three weekly Friday tapes. On the fourth Friday, you use a monthly tape. The number of monthly tapes determines the depth of the backup. This strategy is more complex but yields a backup depth of a full year using just 19 tapes. A simpler strategy with the same name uses three tapes for each day and rotates the three sets.

The incremental rotation (Table 3) strategy is simple to implement and to extend. This plan uses nine tapes, numbered 1 through 9. In the first week, back up to 1, 2, 3, 4, and 5. In the second week, pull tape 1 out of the rotation and use tapes 2, 3, 4, 5, and 6, and so on. Use tape 1 again in the sixth week, when you back up to tapes 6, 7, 8, 9, and 1. Each week, take the Monday tape out of circulation, and it remains completely out of circulation for the following four weeks. For greater backup depth, just add more tapes. At any time, you can move the Monday tape to archival storage and swap in a new tape.

The Towers of Hanoi (Table 4) strategy offers the greatest backup depth using the fewest tapes. The pattern of tape use in this strategy matches the order of moves in the logic game of the same name. The duration of this scheme is 2 raised to the power of the number of tapes, minus 1. For example, five tapes would yield a 31-day rotation (25-1). To schedule this rotation, label the tapes A through E and mark off 31 spaces, one for each day. Write A in every other space. Write B in every other of the 15 spaces that are still empty. Write C in every other one of the 7 spaces that remain. D goes in every other one of the 3 still-blank spaces, and E in the single space left in the middle.

For each day in the rotation, back up to the specified tape. With just five tapes, this strategy has a depth of up to one month, and every added tape doubles the depth. The disadvantage is that the A tape gets twice as much wear as the B tape, and so forth. More important, the complexity can be daunting.