Backup: Why and How? Part 2
By: Walter Metcalf
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.
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.
There are two kinds of "modified backups," and the difference between
them is significant: differential and incremental.
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.
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
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.
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:
We have already mentioned BackMaster
3.0 and BackMaster Ultra.
Some of the main features of BackMaster 3.0 are:
Support for wide variety of devices, especial low-end Jumbo tape drives.
Features DOS-compatible mode in which a DOS restore program can read BackMaster-created
Winner of the OS/2 e-Zine 1997 Readers'
Choice Runner-up Award.
For information regarding BackMaster Ultra, see David Wei's review
in the May 2, 1998 issue of OS/2 e-Zine.
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:
Supports wide array of high-end SCSI, and now ATAPI (IDE), tape drives.
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.
Contains powerful cataloging and backup set system which eliminates setup time for
backups and restores.
Still under active development with updates and patches regularly being released
and posted to the CDS website.
Winner of OS/2 e-Zine 1997 Readers'
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.
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.
Actual painfree backup example.
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.
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.
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!
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.
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
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.
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.
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.
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.
For the next 13 days let the computer perform differential backups as usual.
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.
For the next 13 days let the computer perform differential backups as usual.
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.
Go to step 3.
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
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