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September 2002

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BackAgain/2000 Server Edition version 3.0 - A Review, Part 4

By Walter Metcalf © September 2002


In the previous article in this series we covered the Restore process, including the Disaster Recovery technique. We saw that BackAgain/2000 gives the user several different techniques, so that he or she should be able to recover the data no matter how it was destroyed. However this data is only as secure as the method used to handle the backup media--usually tape. Sloppy handling can render the most sophisticated software and backup procedures completely useless.

Therefore in this installment, we will look at several methods used or recommended by experts to preserve the integrity of data that has been carefully backed up.

Software Methods

Before continuing any further, I feel the need to decide the matter of which software setting our backups should be based on. As you probably know, BackAgain/2000, like almost all backup software programs, contains both an "incremental" and a "differential" setting, which can be used essentially interchangeably. For a refresher on these two backup techniques, please click here.

The typical backup series consists of one or more full backup operations, followed by a large number of differential or incremental runs--usually one per day until the end of a certain period of time.

Although using incremental backups saves a considerable amount of tape space, it suffers from the great disadvantage that there is no redundancy. If one block of one tape is damaged or recorded improperly, the entire SET may be completely ruined. So unless your budget is extremely tight or your tape drives extremely slow, I highly recommend you always use differential backups. Not only does this provide redundant protection against errors, but it gives you multiple versions of volatile files, which can often save the day. For the rest of this article, differential backups will be always used in place of incremental backups unless otherwise stated.

Here is a table to help clarify the differences between the different types of backup methods.

Types of Tape Backups
Full All selected files are backed up.
files marked as backed up.
Copy All selected files are backed up;
does not mark files as backed up.
Differential Backs up only selected files that have changed since last full backup;
files not marked as backed up.
Incremental Backs up selected files that have changed since last full or incremental backup;
files marked as backed up.

Backup Solutions

Tape backup systems usually consist of a pool of tapes divided into groups. Each group contains enough tapes to back up your disks for the chosen period of time (e.g. a week; two weeks; or a month).¹

    Here are some of the more common strategies used to back up disk systems.

  1. One of the most popular backup solutions is the simple Rotation strategy. This involves a series of infrequent (e.g. monthly) full backups and a much more frequent partial backups (e.g. differential or incremental). These partial backups are usually done on a daily or even more frequent basis. Here is the basic procedure:
    1. This strategy requires multiple sets (i.e a collection) of carefully labelled tapes or other media.
    2. Each tape will have two designations on it--the set number (or letter) and the tape number or letter. This designation should appear both on the paper label and on the magnetic label generated by the machine.
    3. If this labelling is not carefully maintained, it will be easy to get the tapes mixed up and cause data destruction.
    4. Fortunately Backup/2000 has several features that tend to remind us to label tapes, and also reduce the chances of data destruction.

      As a specific example, let me describe the procedure I use on my home system:

      1. My main system has two 40 GB hard drives, which are about 40% empty. Of course that number is shrinking. However I have two other systems connected to the main system on a LAN, and my wife has a small PC also on the LAN. I want to provide back up for all these computers, so I need something reasonably husky. I chose a Sony 9000SI which is a DDS-3 internal SCSI drive. Backup capacity is 12 GB native or 24 GB compressed; the drive features hardware compression and self-cleaning.

      2. My tape collection currently consists of 3 sets of 3 tapes each. Each tape is 4 mm in width and 125 meters in length. They hold 12 GB uncompressed data when used with a DDS-3 tape drive. Each tape is labelled, both on the external plastic and the internal magnetic, label with an expression of the type DSs Tt, where "s" is the set number and "t" is the tape number within the set; "DS" is short for "DDS" a sample label would be DS1 T1.

      3. Here's how I use my collection of tapes:
        1. On the first weekend of each month, I remove the current tape from the drive and store it along with the others of the same set. Then I select Tape 1 of the next Set (or Set 1 if the tape removed from the drive was in the last Set in the collection.) I make sure the write button on the tape is moved to the "write" position and insert it in the tape drive. I start BackAgain/2000 and select the FULL_LAN SET.
          1. Note: I generally do this at the end of the day after shutting down all programs currently running. The number of files on the LAN have reached the point where they will not fit on one drive, so that the next day when I first come to the machine I will see a message asking for a second tape. I remove the current tape from the drive, select Tape 2 of the current Set from the tape cabinet, make sure the write button is moved to the "write" position, and insert it in the drive.
          2. After positioning the tape at the beginning and determining the tape is not blank, BackAgain/2000 will ask permission to erase the tape, and then ask for a new label. I type in a new label like "DS1 T2" making sure this corresponds exactly to what is on the tape's external plastic label.
            • Note: BackAgain/2000 does this every time a new tape is inserted into the drive.

        2. For the rest of the month, BackAgain/2000 Scheduler automatically performs a differential backup for each system logged onto the LAN using another SET file called DIFF_LAN.BST. This operation is performed at 3:00 a.m. every day of the week. In the next article in this series, I'll demonstrate in detail how to set this up as well as outline a dependable technique for backing up your entire LAN.

          Here's a summary of the above procedure in tabular form:

          Rotation Backup Cycle
          Set 1
          Set 2
          Set 3
          Sunday Full Backup
          DS1 T1-T2
          Full Backup
          DS2 T1-T2
          Full Backup
          DS3 T1-T2
          Monday Diff Backup
          DS1 T2-T3
          Diff Backup
          DS2 T2-T3
          Diff Backup
          DS3 T2-T3
          Tuesday Diff Backup
          DS1 T2-T3
          Diff Backup
          DS2 T2-T3
          Diff Backup
          DS2 T2-T3
          Wednesday Diff Backup
          DS1 T2-T3
          Diff Backup
          DS2 T2-T3
          Diff Backup
          DS2 T2-T3

        3. Currently a month's backup, as I have described above, will usually fit onto the 3 tapes provided in each tape set. However, occasionally this is not the case, and the tapes run out before it is time for another full backup. Therefore I have ordered enough additional tapes to increase my backup collection to 4 sets of 4 tapes each. Note the almost insignificant cost of the new tapes. (<$10 US), compared to the much higher price ($38US) for Travan tapes. This reinforces what I mentioned earlier: that DAT tape drives are a better buy if:
          1. you can afford them;
          2. if you have a reasonably large file base on your hard drives; or
          3. if you need to back up a LAN.

        4. Needless to say there is nothing "magical" about the period of a month. In fact I suggest you start with a period of two weeks or even a week until you have your procedures (both manual and computer) established and are comfortable with their reliability. A month can represent a large amount of vulnerable data if your backup routines are flakey. Once things have been running smoothly for several weeks you can increase the size of the period. However the backup period should never go above your "comfort level".

        5. In my opinion, the rotation strategy is the preferred strategy in most cases for the home or home-office user.

  2. There are several modifications to the Rotation strategy that could be added to the basic one as described above.

    1. Offsite storage.
      1. Those with very sensitive data, such as payroll information or trade secrets, should arrange to place one of the sets or a copy of one of the sets in a secure offsite location. An offsite location must meet at least the following requirements:
        1. It must be in a different building. If you live in an apartment in the same building as your business, and make the offsite location your apartment, what happens if the building is severely damaged in a fire? You may still lose your data!
        2. It needs to readily accessible whenever your business is open.
        3. If it is in a location controlled by someone else, e.g. at a bank or a friend's, it should be kept in a safety deposit box or some other secure location reserved for your documents and tapes alone.
        4. While putting your tapes or other media in an onsite safe may help safeguard your data from burglars, a safe is no substitute for off-site storage. In the event of fire, the interior of the safe is likely to get hot enough to ruin your tapes.
    2. Grandfather-Father-Son.
      1. Depending upon the periods chosen, this strategy can provide the backup procedure with the greatest degree of redundancy of all. Although disk-based devices, such as CD-RW, are possible, tapes are normally chosen because the G-F-S is a rotation scheme in which the media have to be rotated through different positions in the rotation scheme. Essentially this is like a simple Rotation strategy , but with calendar restraints added to it. For more details, click here. Maintaining correct labelling is absolutely essential with this technique.
    3. Tower of Hanoi.
      1. This is yet another rotation scheme, based on a mathematical game. For details, click here.
    4. Cleaning.
      1. Tapes, CDR's, and DVD-R's are all unsealed devices (as opposed to the hermetically sealed hard drive), and therefore their read heads are exposed to dust, smoke, and other foreign material. Therefore they must be cleaned from time to time.
      2. The method of cleaning depends on the type of media or cartridge. The DAT cartridge is one of the most sophisticated of all in that it has built-in cleaning brushes which pass over the heads every so-many reads or writes. However the brushes themselves must be cleaned occasionally. When brushes become completely dirty, the tape unit turns on a specific LED-display on the console. The brushes can then be quickly cleaned by inserting a special cleaning cartridge.
      3. Regardless of the type of backup tape or media you are using, carefully read the cleaning procedures and build a cleaning cycle into your backup procedures. The most common reason for failures during tape reads or writes during backups is dirty heads!
    5. Retensioning
      1. A procedure less well-known than cleaning is retensioning. This applies only to tapes. After a number of uses, some parts of a tape can become more tightly wound on the cartridge than other. This will cause the tape to be stretched, and will make the index marks on the tape to become inaccurate enough that the drive will be unable to find the data it originally wrote there, or be unable to locate the block number where it is supposed to write the data. This will produce a read or write fault error.
        • To prevent such errors by keeping the tapes evenly wound on the cartridge, it is a good idea to automatically retension tapes the first time they are inserted into the cartridge. To do this for Tape 1 of each Set, select Options | Media | Retension media before backup. In order to do it for the other tapes in a Set, you would need to set the backup as a CMD or REXX file and put the Retension command just before the partial backup command.

          Here is a sample batch file to retension a tape, erase it and then run the command line backup.

          REM This is a simplified example of a batch file which Retensions a new tapes before a differential backup is performed on it.
          REM Come here to perform the first differential backup on a new tape.
          REM WAIT Until tape comes to ready position
          CLTAPE SCSI:0 WAIT
          REM Retension the new tape.
          REM Erase the new tape. A confirmation window will be raised.
          REM Perform the differential backup.
          CLBACK -ir E:\* -d ScsiTape:0 -set DIFF_LAN.BST -type diff
          REM Exit the program

  3. Another strategy popular with some people and businesses is to backup software and data separately. The software (e.g. system, compilers, database software) is backed up infrequently, perhaps only once or only when new updates are released by the manufacturer. The data on the other hand is backed up very frequently, at least daily.
    1. One problem inherent in this strategy is the difficulty in separating data from software. The strategy works best if the two types of information are kept in different areas of your hard drive systems, e.g. different logical drives. However some popular business systems such as Lotus SmartSuite make this somewhat difficult to do.
    2. Another problem is that for developers, the line between data and software can be almost non-existent.
    3. However there are many businesses which only run a small number of software products on their sites, and relatively large amounts of data either being typed in or being entered through POS terminals or the internet.
      1. Video stores, fast-food enterprises, and independent grocers make good examples of this type of business.
      2. In this type of business it might make sense to backup the operating software when it is installed, make a spare copy, and refresh the backups when the software is updated. However, the data for this type of business is far more valuable to the organization and should be backed up separately at least once a day.

  4. The Desktop

    1. For many OS/2 and eComStation users the Desktop is the most volatile portion of their system and is unfortunately also one of the most critical. Serious corruption to the Desktop can require complete reinstallation of OS/2. Unfortunately, the Desktop is not stored in one location on the system disk, but is scattered in about four different locations. Consequently the usual backup procedures may not afford sufficient protection against Desktop corruption. There are, however, two measures you can take in addition to the regular backup procedures that will secure your Desktop.
      1. Back it up separately using tools specifically designed for the purpose. Two such tools are.
        1. WPTOOLS by Henk Kelder; and
        2. UniMaint by Sierra HyperStar Software

          WPTools is freeware and UniMaint is a commercial product, current price=$65 US. For many that alone would decide the issue. However, UniMaint has such a wealth of tools besides Desktop backup that I have not for one minute regretted purchasing it.

      2. Restrict the contents of your system drive to the files necessary to run your system. Keep other software such as browsers, Java, and application drivers on other logical drives. This will make it quick and easy to restore your system drive from tape should you not be able to get your system started using other methods.

In the next article we will complete our series by looking at how to set up an automatic, worry-free, reliable backup of a LAN. Please join me then. In the meantime, if you have any questions or comments about this article, please feel free to email me.

¹As mentioned earlier, tapes aren't the only media that can be used. If your disk drives aren't too large, then CDR, CD-RW or even DVD-R become a practical alternative. Tapes are popular because disk capacity on even home systems are becoming quite large, and TRAVAN and DAT tapes provide the capacity needed. The downside is the cost of the drive. A good DAT drive, for example, is well over $500 US. They can cost a lot more if you want extra features like auto-changing or unusually large capacity. TRAVAN drives are less expensive, but the tapes cost more and hold less data.

BackAgain/2000, version 3.0
Developer: Computer Data Strategies, Inc.-
Price: Workstation Edition $99.00, Upgrade from v2.1: $79.00
         Server Edition $199.00, Upgrade from v2.1: $149.00

Other links referenced:
   Part I of this review -
   Part 2 of this review -
   Part 3 of this review -

Additional Reading:

Article by this writer showing the importance of backing up.
   Backup: Why and How? Part 1 -
   Backup: Why and How? Part 2 -

Series by writer detailing procedure for backing up a LAN.
   How to Back Up Your Network, Part 1 -
   How to Back Up Your Network, Part 2a -
   How to Back Up Your Network, Part 2b -
   How to Back Up Your Network, Part 3 -

Excellent article by Hewlett-Packard outlining several backup strategies.
   Developing a Backup Strategy -

Walter Metcalf has written many articles on the use and usefulness of OS/2 and eComStation. He was widely known as the Guide for the " OS/2" site until its unfortunate plug pulling. Walter has served as President of VOICE and is currently the Co-ordinator of VOICE's Warp Doctor project You can read more of Walter's articles in the archives of the VOICE Newsletter and many of his previous articles at his personal web site

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