TAILIEUCHUNG - Networking: A Beginner’s Guide Fifth Edition- P39

Networking: A Beginner’s Guide Fifth Edition- P39:I have run into many people over the years who have gained good even impressive working knowledge of PCs, operating systems, applications, and common problems and solutions. Many of these people are wizards with desktop computers. | 172 Networking A Beginner s Guide TIP If your data is extremely critical and not easily reconstructed you can often perform full backups every night and also squeeze in a quick incremental backup midday. This way you can t lose more than a half day s worth of data. You can also choose rotation schemes that are simpler than GFS. For instance you may use just two or three tapes and then rotate them in sequence overwriting the old data each time you do so. This lets you restore any of the previous three days data. The shortcoming of this scheme is that you may need to go back further in time to restore data that was erased or damaged without anyone immediately noticing. You can combat this problem by using several tapes that you rotate weekly or monthly. One factor to keep in mind when considering different tape rotation schemes is the granularity of your backups. Generally granularity refers to the flexibility that you retain to recover data from earlier tapes. In the standard GFS scheme where full backups are made all the time you could restore a file from any given day for a week s time for any given end of the week Friday for a month s time or for any given month for a year s time. You could not however restore a file that was created three months ago in the middle of the month and erased or damaged before the month was over because a clean copy wouldn t exist on any of the backup tapes. The best advice for choosing a rotation scheme for important data is that unless there are reasons to do otherwise as already discussed use the GFS scheme with full backups. This maximizes the safety of your data maximizes your restoration flexibility and minimizes the risk of media failure. If other factors force you to choose a different scheme use the discussions in this chapter to arrive at the best compromise for your situation. Granularity and Data Corruption A Tricky Balance One reason to consider granularity carefully is the possibility of data becoming corrupted and the .

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