BackAgain/2000 Server Edition version 3.0 - A Review, Part 4
Introduction
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.
-
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:
-
This strategy requires multiple sets (i.e a collection) of carefully labelled
tapes or other media.
-
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.
-
If this labelling is not carefully maintained, it will be easy to get the tapes
mixed up and cause data destruction.
-
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:
-
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.
-
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.
-
Here's how I use my collection of tapes:
-
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.
-
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.
-
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.
-
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
|
January
|
February
|
March
|
|
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
|
....
|
....
|
....
|
....
|
-
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:
-
you can afford them;
-
if you have a reasonably large file base on your hard drives; or
-
if you need to back up a LAN.
-
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".
-
In my opinion, the rotation strategy is the preferred strategy in most cases for
the home or home-office user.
-
There are several modifications to the Rotation strategy that could be added to
the basic one as described above.
-
Offsite storage.
-
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:
-
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!
-
It needs to readily accessible whenever your business is open.
-
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.
-
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.
-
Grandfather-Father-Son.
-
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.
-
Tower of Hanoi.
-
This is yet another rotation scheme, based on a mathematical game. For details,
click here.
-
Cleaning.
-
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.
-
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.
-
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!
-
Retensioning
-
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
REM Come here to perform the first differential backup on a new tape.
REM
REM WAIT Until tape comes to ready position
CLTAPE SCSI:0 WAIT
REM Retension the new tape.
CLTAPE SCSI:0 RETEN
REM Erase the new tape. A confirmation window will be raised.
CLTAPE SCSI:0 ERASE
REM Perform the differential backup.
CLBACK -ir E:\* -d ScsiTape:0 -set DIFF_LAN.BST -type diff
REM Exit the program
EXIT
-
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.
-
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.
-
Another problem is that for developers, the line between data and software can be
almost non-existent.
-
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.
-
Video stores, fast-food enterprises, and independent grocers make good examples
of this type of business.
-
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.
-
The Desktop
-
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.
-
Back it up separately using tools specifically designed for the purpose. Two such
tools are.
-
WPTOOLS
by Henk Kelder; and
-
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.
-
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.
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 "About.com 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 http://www.warpdoctor.org. You can read more of Walter's articles in the archives of the VOICE Newsletter and many of his previous os2.about.com articles at his personal web site http://www.wmetcalf.com.
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