1. Backups Backups are essential for recovering from – mistakes deleting a file by accident making changes to a document or file that turn out to be undesirable – disasters house burns down thief steals all computer equipment on premises – failures hard drive fails file becomes corrupted filesystem fails

2. Backup Considerations Frequency of backup – how often you back up determines how much work you can lose Number of backups – how many backup copies you have (at least one off site) determines how resilient you are to failures of backups themselves Age of backups – it is not good enough to have 3 copies if they are all less than a week old!

3. Backups (cont'd) Because of the disaster category, there is a wise saying, " if it's not off site, it's not backed up " A copy that is stored on the same device will disappear along with the original if the device or file system fails or is stolen

4. Automatic Backups Example, Windows Backup – back up daily, weekly(default), or monthly (frequency) – keep backups until you delete them (aging) Example, Apple Time Machine – backs up every hour (good frequency) – retains the following (good aging) every hour for a day every day for a week every week thereafter when backup drive is full, it removes oldest backups to make space for new backups

5. Backup Retention It is not good enough to keep just one backup, because you may not discover a problem until both the working copy and the backup copy have the problem At least several backups of increasing age need to be retained A file that's accidentally deleted in March and discovered to be missing in June could be restored from February's backup

6. Snapshot-style backups Primarily to recover from mistakes or undesired changes as you work Make a copy of a file before you change it Make a copy of a file while you are making changes After you're happy with the changes and you feel the work is "stable", there is no need for the copy, which is often on the same drive

7. Snapshot-style backups (cont'd) Different ways to preserve a snapshot of your work: – Copy the file with Windows Explorer – Copy the file with the command line copy command – Use your application's "Save as" feature, but remember this usually means you're now working on the newly named copy

8. Ad Hoc backups For large datasets (eg 10TB) – store a copy (set of hard drives?) in a secure off- site location – keep a copy or two on site – keep track of the incremental changes – every once in a while (weekly, monthly, or yearly, for example) apply the incremental changes to a local copy, and trade that with the off site copy

9. Windows Backup Windows backup will wait for the next backup if the computer is asleep Possible solution In Windows 7: – go to control panel\power options – edit plan settings – click the link "change advanced power settings" – In the tree expand "sleep" – "allow wake timers" option.

10. Backup Management You must be organized with your backup system All (external) backup devices need to be labeled with the date and contents so they may be properly rotated (it's not feasible to keep every backup forever)

11. Backup Security Anyone who has access to the backup devices (hard drives, tapes, DVD's, etc) also has access to all the most sensitive data on them Encrypting the backups can alleviate this problem, but this adds a new dimension of managing encryption keys, which is non-trivial in itself Backups need to be stored physically secure and/or encrypted