Backup Types


When your hard drive fails, the drive can be replaced, but the data cannot. That’s where backups come in. There are different ways of backing up depending on the amount of data you are backing up.

Online Backup

This method is becoming increasingly popular way of  backing up data over the internet. An article I wrote shows how to be your own online backup provider.
Full backup

A full backup, which Microsoft calls a normal backup, backs up every selected file, regardless of the status of the archive bit. When the backup completes, the backup software turns off the archive bit for every file that was backed up. Note that “full” is a misnomer because a full backup backs up only the files you have selected, which may be as little as one directory or even a single file, so in that sense Microsoft’s terminology is actually more accurate. Given the choice, full backup is the method to use because all files are on one tape, which makes it much easier to retrieve files from tape when necessary. Relative to partial backups, full backups also increase redundancy because all files are on all tapes. That means that if one tape fails, you may still be able to retrieve a given file from another tape.
Differential backup

A differential backup is a partial backup that copies a selected file to tape only if the archive bit for that file is turned on, indicating that it has changed since the last full backup. A differential backup leaves the archive bits unchanged on the files it copies. Accordingly, any differential backup set contains all files that have changed since the last full backup. A differential backup set run soon after a full backup will contain relatively few files. One run soon before the next full backup is due will contain many files, including those contained on all previous differential backup sets since the last full backup. When you use differential backup, a complete backup set comprises only two tapes or tape sets: the tape that contains the last full backup and the tape that contains the most recent differential backup.
Incremental backup

An incremental backup is another form of partial backup. Like differential backups, Incremental Backups copy a selected file to tape only if the archive bit for that file is turned on. Unlike the differential backup, however, the incremental backup clears the archive bits for the files it backs up. An incremental backup set therefore contains only files that have changed since the last full backup or the last incremental backup. If you run an incremental backup daily, files changed on Monday are on the Monday tape, files changed on Tuesday are on the Tuesday tape, and so forth. When you use an incremental backup scheme, a complete backup set comprises the tape that contains the last full backup and all of the tapes that contain every incremental backup done since the last normal backup. The only advantages of incremental backups are that they minimize backup time and keep multiple versions of files that change frequently. The disadvantages are that backed-up files are scattered across multiple tapes, making it difficult to locate any particular file you need to restore, and that there is no redundancy. That is, each file is stored only on one tape.

Backup Media

Another consideration is which media to save you data on. The popular media formats are:

Tape
Optical Drive (DVD, BluRay)
Hard Disk

Hard disk backup seem to becoming more popular because the price of disk is falling and it is the fastest method. Tape has been around for a while and is a durable media and can store a large amount of data. The problem I see with both disk and tape is that they are both subject to magnetic fields. Optical drives such as DVD and BluRay writers don’t store as much data on a single media but in my opinion is the most durable for long term storage. Although the argument can be made that all you need is the last backup to restore the data, but I like to keep a few versions just in case.

Whichever method of backup or whichever media you use, backup often to save yourself a headache.

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