CompTIA Security_ Deluxe Study Guide_ SY0-201 - Emmett Dulaney [211]
Many organizations have taken the position that backing up user files is the user’s responsibility. Although this policy decision saves administrative time and media, it isn’t a good idea. Most users don’t back up their files on a regular basis—if at all. With the cost of media being relatively cheap, including the user files in a backup every so often is highly recommended.
Applications Applications such as word processors, transaction systems, and other programs usually don’t change on a frequent basis. When a change or upgrade to an application is made, it’s usually accomplished across an entire organization. You wouldn’t necessarily need to keep a copy of the word-processing application for each user, but you should keep a single up-to-date version that is available for download and reinstallation.
Some commercial applications require each copy of the software to be registered with a centralized license server. This may present a problem if you attempt to use a centralized recovery procedure for applications. Each machine may require its own copy of the applications for a recovery to be successful.
Knowing the Backup Types
Three methods exist to back up information on most systems:
Full backup A full backup is a complete, comprehensive backup of all files on a disk or server. The full backup is current only at the time it’s performed. Once a full backup is made, you have a complete archive of the system at that point in time. A system shouldn’t be in use while it undergoes a full backup because some files may not get backed up. Once the system goes back into operation, the backup is no longer current. A full backup can be a time-consuming process on a large system.
During a full backup, every single file on the system is copied over, and the archive bit on each file is turned off.
Incremental backup An incremental backup is a partial backup that stores only the information that has been changed since the last full or the last incremental backup. If a full backup were performed on a Sunday night, an incremental backup done on Monday night would contain only the information that changed since Sunday night. Such a backup is typically considerably smaller than a full backup. Each incremental backup must be retained until a full backup can be performed. Incremental backups are usually the fastest backups to perform on most systems, and each incremental backup tape is relatively small.
An incremental backup backs up only files that have the archive bit turned on. That is how it can identify which files have changed or been created. At the conclusion of the backup, the archive bit is turned off for all the files that were included in the backup.
Differential backup A differential backup is similar in function to an incremental backup, but it backs up any files that have been altered since the last full backup; it makes duplicate copies of files that haven’t changed since the last differential backup. If a full backup were performed on Sunday night, a differential backup performed on Monday night would capture the information that was changed on Monday. A differential backup completed on Tuesday night would record the changes in any files from Monday and any changes in files on Tuesday. As you can see, during the week each differential backup would become larger; by Friday or Saturday night, it might be nearly as large as a full backup. This means the backups in the earliest part of the weekly cycle will be very fast, and each successive one will be slower.
A differential backup backs up only files that have the archive bit turned on. At the conclusion of the backup, the archive bit is left on for those files so they are then included again in the next backup.
When these backup methods are used in conjunction with each other, the risk of loss can be greatly reduced, but