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Frequently Asked Questions (FAQ) 1. What are the benefits of using the Towers of Hanoi backup rotation strategy? 2. How does the Towers of Hanoi backup rotation strategy work? 3. Are there any downsides to using the Towers of Hanoi backup rotation strategy? 4. Can I do differential or incremental backups with SaraB? 5. Can SaraB implement the Grandfather-Father-Son rotation strategy? 6. I use SaraB to backup to a remote machine. Are my backups safe enough? 7. How do I get SaraB to run automatically? For instance, if I want to do daily backups. 8. Can I run multiple configurations of SaraB on the same system? 10. How did you come up with the name, SaraB? 11. Isn’t the Towers of Hanoi a game? ********************************************************* Once SaraB is started, it uses three configuration files (sarab.conf, sarab.dcf, rotation.schedule) to decide how to create and rotate backups. Each backup is stored in a directory, which logically represents a media-set of tapes. I call these directories "virtual-tapes". The virtual-tapes are then automatically rotated (according to rotation.schedule) to use disk space efficiently and to ensure that your backups are stored for the length of time that you desire. 1. What are the benefits of using the Towers of Hanoi backup rotation strategy? The Tower of Hanoi strategy is the most effective backup rotation method for creating the longest possible recovery situation with a limited amount of backup media. To calculate how long a given number of virtual-tapes will cover, use the formula 2^n – 1. Raise 2 to the number of virtual-tapes, and subtract 1. For example, five backups would yield a 31-day rotation (2^5-1). If you used 10 virtual-tapes with the Towers of Hanoi rotation strategy, you would have backup coverage for 1023 days, nearly three years! This rotation would have backups from 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 and 1023 days ago. Traditionally, the Towers of Hanoi strategy was only used if an organization could afford an expensive auto-loader tape drive. This is because the technique is considered too complex to rely on manual rotation. Other problems come from uneven wear and tear on the magnetic tapes. These tapes had to be replaced on a complex schedule, depending on how often the tapes were used. These problems are eliminated when the backup media is a hard drive, such as with SaraB. This is because a hard drive has random-access, can store much more data, and can be used repeatedly without physical degradation. SaraB takes care of the complex rotation strategy, so administrators can now get the benefits of this strategy without spending any money! (Unless you decided to purchase a new 300 GB hard drive to store your archives on.) 2. How does the Towers of Hanoi backup rotation strategy work? The links below provide good information about the Towers of Hanoi and other rotation strategies, as well as knowledge about archiving data in general. Backup Nice and Easy (PC Magazine) 3. Are there any downsides to using the Towers of Hanoi backup rotation strategy? The main downside to using the Towers of Hanoi strategy is that it doesn’t provide a large number of short-term backups. This may be important, depending on the needs of your organization. For example, using the Grandfather-Father-Son strategy with 10 virtual-tapes, there is an effective short-term recovery with seven daily backups.. However, the Towers of Hanoi would only have daily backups for two days. This may not be a problem, depending on the needs of your organization. I feel that SaraB provides a cheap way to implement a rotation strategy that has not previously been available to small organizations before. If your network needs more short-term backups, you can implement a G-F-S example, or create your own custom rotation.schedule. 4. Can I do differential or incremental backups with SaraB? You can perform both differential and incremental backups, provided that you have configured rotation.schedule to perform them. 5. Can SaraB implement the Grandfather-Father-Son rotation strategy? Yes, SaraB can implement the Grandfather-Father-Son. Didn't you read the front page? The main benefit of the G-F-S strategy is that it provides more short-term backups than the Towers of Hanoi. With SaraB, you can choose the rotation strategy that best meets your needs. 6. I use SaraB to backup to a remote machine (via NFS or SAMBA). Are my backups safe enough? It depends on your needs and your environment. For example, if your network was hacked into, would your backups be safe? What about during a malicious virus outbreak? For additional assurance, you may want to periodically copy your backups to removable media such as magnetic tape or DVD (Hint: Configure SaraB to create slices the same size as your removable media.) Perhaps you should even take the removable media to an off-site location for extra safety. It all depends on what your needs are. For more information on disaster recovery, I recommend reading UNIX: Backup and Recovery, by W. Curtis Preston. You should also visit the links that are listed under question #2. 7. How do I get SaraB to run automatically? For instance, if I want to do daily backups. You need to manually create cron jobs that will schedule SaraB to run automatically. Please read the install document to learn more about this. 8. Can I run multiple configurations of SaraB on the same system? Yes, you can. :) Starting with version 0.2.2, you can specify the configuration file to be used as a parameter to "sarab.sh". Example: /usr/local/sarab/sarab.sh /etc/sarab/server2/sarab.conf Thanks to Joseph Watson for suggesting this feature. SaraB does not include any method for restoring a backup. To restore your data, use KDar (KDE Disk Archiver) for a nice GUI interface, or simply use DAR commands (see DAR documentation). To locate the directory that holds the data you want to restore, sort the directories by the time they were created. To do this, type "ls -Alt" in the directory where your backups are located. Use the time-stamps on the backup directories to select which backup you want to restore from. If the backup was a differential or incremental, read the reference_archive.txt file included in the virtual-tape to learn which virtual-tape was used as the referential archive. You can also view the SaraB logs to find out when each backup was run. 10. How did you come up with the name, SaraB? This project is not named after an ex-girlfriend, or for the Iranian town of the same name that is known for its Persian rugs. I originally called this project Tohbr, for “Towers of Hanoi Backup Rotation”. Tohbr was hard to remember, and it did not provide a good description of what SaraB can do (it supports more than just the TOH strategy). My next idea was to name the project Scarab, for “SChedule And Rotate Automatic Backups”, but the name was already taken. I thought Scarab would be such an appropriate name for a backup-related program, since the scarab beetle has been considered a symbol of spontaneous generation, new life, and resurrection. I can imagine that these feelings are similar to what network administrators experiences when their backups successfully save their job! You should consider SaraB to represent a reliable employee who is responsible for starting your backups, rotating the tapes, and generally automating the process so you don’t have to worry about it! (The name “SaraB” is also similar to "AMANDA", a popular tape backup program. Perhaps they are distant cousins?) 11. Isn’t the Towers of Hanoi a game? Yes, it is. The pattern of tape rotation in this strategy matches the order of moves in the logic game of the same name. In addition, most beginning Computer Science students should have implemented this as a homework assignment. An example of 2^n-1. |
