Backup: Why and How? Part 2

By: Walter Metcalf
Date: 09/01/99

Last week we looked at some of the reasons why regular system backup is necessary. I hope you are now convinced it is essential to your peace of mind and the safety of your data. This week we'll look at the methods found in the backup literature (e.g. BackAgain/2 Professional User Guide, by Computer Data Strategies, pp. 18-21 and "Backup Basics", by Hewlett-Packard) and then I tell you which I think is best and why. Next we'll quickly review some of the excellent OS/2 software available today, Finally I'll detail the procedure I have found produces the best results.

  1. First, both the sources above deal with strategies for backup. The general idea in all cases is to backup all your files to tape (a "full backup") every week or perhaps two weeks. On each of the other days you perform "modified backups," perhaps on a different set of tapes, each day. At the end of each week either make an additional backup for off-site storage or take the set of tapes for the previous week and move them off-site.

    1. There are two kinds of "modified backups," and the difference between them is significant: differential and incremental.

      1. A differential backup backs up files which have been modified since the last full backup. It is performed by setting the backup software to leave the file's archive flag unchanged after it is backed up. The differential method of backup (1 full backup + several differential backups) has two main advantages: 1) it causes redundancy so that a modified file is likely to be found on more than one backup set; and 2) any file can be restored by going to at most two known backup sets--the original full backup and the most current differential backup. Indeed the entire disk can be safely restored by restoring just the full backup and the latest differential backup. The differential backup method's main drawback is the amount of tape space required for the differential backups, especially near the end of a cycle.

      2. An incremental backup backs up only those files which have been modified since the last backup, either full or incremental. It is performed by setting the backup software to clear the file's archive flag after it is backed up. The incremental method of backup (1 full backup + several incremental backups) has one main advantage: it requires the minimum tape space possible. The incremental backup method has one serious disadvantage: it is generally necessary to read several tape backup sets to find the file you need. To restore an entire disk it's necessary to restore the full backup and then restore every incremental backup in the cycle.

        In a nutshell, the differential backup method yields optimal restore efficiency and effectiveness and the incremental backup method yields optimal backup efficiency.

    2. Personally, painful experience has shown me that incremental backups are simply not sufficiently reliable. So I use the differential backup method on a biweekly cycle. My system is not that large (2.2 GB hard drive space) and I am able to put an entire cycle on one Travan 8 GB (TR-4) tape when the backup software is set for compression. I don't use separate tapes because, quite frankly, I don't have the resources; in any case I have found the present system very satisfactory. However, for added security, I do want to extend the rotation to 3 weeks so that each tape is only used every third cycle. Then I'll be able to keep one cycle's backup near the machine and other off-site.

      Tip: Get the biggest and fast backup drive you can possibly afford. Borrow if you have to. I mean it! With the size of today's and tomorrow's disk drives, the Jumbo and Travan 1 drives, for example, are simply too small and slow for all but the smallest of systems.

  2. If you started using OS/2 in 1993 and believed backup was essential, as I did, you would have found life very frustrating: I certainly did! Reliable OS/2 tape backup software was about as scarce as the proverbial hen's teeth! The only one I could find was BackMaster 1.01A by MSR Development. Unfortunately it was a very early immature product and therefore had more than its share of problems. I hasten to add that MSR's newest products, BackMaster 3.0 and BackMaster Ultra, have improved considerably since those early days. MSR is to be commended for its early commitment to the OS/2 platform and for its products' support of an unusually broad array of hardware devices.

    Let's look briefly at three of the backup software products available today:

    1. We have already mentioned BackMaster 3.0 and BackMaster Ultra. Some of the main features of BackMaster 3.0 are:

      1. Support for wide variety of devices, especial low-end Jumbo tape drives.
      2. Features DOS-compatible mode in which a DOS restore program can read BackMaster-created tapes.
      3. Winner of the OS/2 e-Zine 1997 Readers' Choice Runner-up Award.
      4. For information regarding BackMaster Ultra, see David Wei's review in the May 2, 1998 issue of OS/2 e-Zine.

    2. BackAgain/2 Professional from Computer Data Strategies. CDS has created a truly professional, powerful backup solution. As a user for almost 3 years, I can testify to its dependable performance in a wide variety of situations. Some of its main features are:

      1. Supports wide array of high-end SCSI, and now ATAPI (IDE), tape drives.
      2. The only program listed here that resets the archive flags after the backup is complete. (The others perform this operation on the fly.) This feature is crucial if you plan on using the incremental backup method.
      3. Contains powerful cataloging and backup set system which eliminates setup time for backups and restores.
      4. Still under active development with updates and patches regularly being released and posted to the CDS website.
      5. Winner of OS/2 e-Zine 1997 Readers' Choice Award.

    3. Seagate Backup Exec for OS/2 Warp from the Seagate Software. Seagate Backup Exec used to be called Arkada Backup for OS/2 before Seagate bought out Arkada. Overall it is similar to BackAgain/2 which contains all the features of Backup Exec plus some that Backup Exec lacks. One feature the latter surprisingly lacks is a standalone verify; in other words the verify function is an integral part of the restore function. For more information on this product see Noah Sumner's review in the Jan. 16, 1998 issue of OS/2 e-Zine.

    4. Finally, there is one point more important that which tape backup is the best. Whatever the software package is, if it doesn't support your tape drive it is useless! If you already have a tape drive, then download the demos provided on the web for various software products and see which best supports your hardware. If you find several, as you probably will, then use the brief reviews above and other reviews to determine the best for you.

  3. Actual painfree backup example.

    1. As I've already mentioned I use BackAgain/2 Pro, so my example will be based on that product, but the procedures for the others mentioned are similar. This example is to be taken as just that: an example. You may reject it altogether or you can modify it to suit your own hardware configuration. Note also that it is based on the fact that I can get an entire 2 week cycle on one cartridge.

      1. Initialization tasks
        1. Label the number of tapes you plan to rotate. (I use two now, but want to change to three shortly.) Let's say you want to rotate three tapes: A, B, C.
        2. Check your tape drive manual, and if it allows formatting, then format and retension all three tapes. N.B. High-end Travan tapes such as the TR-4 are pre-formatted and self-cleaning and MUST NEVER be formatted or cleaned. Doing so can irreparably damage the tape and possibly harm your drive as well. So check your manual carefully!
        3. Following your backup software instructions, define a SET object to backup all files on all drives and reset the archive flags, i.e. for a FULL backup.
        4. Again following the instructions, define a SET object to backup modified files only on all drives and to leave the archive flags unchanged, i.e. for a DIFFERENTIAL backup.
        5. Follow the your software's instructions to set up an unattended differential backup every day at sometime convenient to you. I leave my computer on all the time, so my backup is set for 4:00 am when I am asleep. With both BackAgain/2 Pro and Seagate Backup Exec, you can do this by dragging the SET object into a special Scheduler folder created when you install the product.

          • Tip: CDS technical support has told me of a bug in some versions of Warp which causes the timers that run scheduler folder operations to be reset. If you are using this method to set up your backups and find your backups are not running this may be why. Trying using one of the more conventional scheduling mechanisms instead. For example, I have set up BackAgain/2 itself by specifying the differential set object in the Configuration|Preferences window; then I leave BackAgain/2 in the system at all times. I dragged and dropped a shadow of BackAgain/2 into the Warp startup folder for those rare occasions when I need to reboot Warp.

      2. On the 1st Saturday (or whatever day of the week you choose) insert Tape A in your drive and perform a full backup. Move Tape B to your off-site location.
      3. For the next 13 days the computer should automatically perform a differential backup with no action on your part. If BackAgain/2 completes normally the backup window disappears; otherwise it remains on the screen signifying there's been a problem. In any case I like to check to make sure the backup was actually performed.
      4. On the 3rd Saturday, remove Tape A and store it safely. Insert Tape B into your drive and perform a full backup. Move Tape C to your off-site location.
      5. For the next 13 days let the computer perform differential backups as usual.
      6. On the 5th Saturday, remove Tape B and store it safely. Insert Tape C into your drive and perform a full backup. Move Tape A to your off-site location.
      7. For the next 13 days let the computer perform differential backups as usual.
      8. On the 7th Saturday, remove Tape C and insert Tape A into your drive and perform a full backup. Move Tape B to your offsite location.
      9. Go to step 3.

    2. The main issue with the above system is that all backups for two weeks are one tape. Remember however that you also have a copy of your data on your hard drive(s). For you to lose a significant amount of data you have to lose all of your hard drive AND the backup tape near the end of the cycle. Therefore two obvious ways of tightening security would be to shorten the cycle--to one week, for example, and to put every backup on a separate tape. Both improve security but come at a price--the extra cost of the tapes. It's up to you decide what balance is best for your particular situation.

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