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AS/400 Backup Status

Posted on 2007-03-28
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Last Modified: 2010-08-05
Hi;

How can I know if my AS/400 backup everything that I need including system and all data?  When I run DSPBCKSTS, I got the following information.

What Was Backed Up                                       Last Backup Date
User Libraries:
    All.................................................................. 03/27/07
    All (changes only)
    From list
    From list (changes only)
Folders:
    All...................................................................03/27/07
    All (changes only)
    From list
User directories:
    All...................................................................03/27/07
    All (changes only)
Security data ....................................................03/27/07
Configuration ....................................................03/27/07
OfficeVision/400 Calendars
OfficeVision/400 mail

I want to make sure if disaster occurs, all data and system files in my backup tape can be restored.

And also, how can I tell...
1. if my backup tape capacity is full
2. the total size of data and system files backed up.

I need these information to determine how many tapes I need for backup each time.
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Question by:KANEWONG
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by:tliotta
tliotta earned 250 total points
ID: 18812892
KANEWONG:

For a start, you'll almost certainly never know if your tape is nearly full without testing. Testing might involve running a program loop that simply wrote tape records after the last saved file until end-of-tape was signalled. Then store the number of records written each day. As more of the tape is used by your saves, the number of tape records that you can write will go down.

Two elements have a large impact -- the number of gaps and the size of the tape records between gaps.

Tape transports have gotten incredibly precise, but they'll never be perfect. The physical speed of moving tape puts stresses on the tape itself and on the hardware. The mechanism tries to start tape moving as quickly as possible and to stop it as quickly as possible. Because this can never happen, tapes records don't generally get written so that one record immediately follows another. Instead, there's a small length of unused tape between each record -- an "inter-record gap".

(Note: DAT tapes don't have these gaps. But they have a couple other elements that also affect swallow up space on the tapes.)

A tape record is essentially a "block". Each block is written and a gap follows. If blocks are small, the number of gaps increases.

The number of objects can influence the number of blocks. A very large number of small objects can take up much more space on tape than a few large objects. Each small object might take up only a partial block, each block has a gap after it. Large objects might completely fill a few full blocks.

When saving a variety of things to a single tape, it can be extremely difficult to figure out how much tape surface was used. Not only inter-record gaps, but various kinds of "tape marks" can also be written. Where does one object end and another begin? If an object takes multiple blocks, the only way to tell what block belongs to which object is to write extra blocks to the tape.

And beyond simple management overhead, stretches of tape might simply be bad and get skipped over. Tape can stretch so that it's a bit longer after it's been used. Tapes might simply be a little bit longer than advertised.

In short, without testing, you probably aren't going to know.

Tom
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by:KANEWONG
ID: 18816710
Hi;

thanks for your comment.

I am currently using DAT on my AS/400e, can I force it to overwrite tape each time I run backup?  And how?
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tliotta earned 250 total points
ID: 18820438
KANEWONG:

DAT is becoming more common fortunately. Best you can do is a simple:

 ==>  dsptap  dev( tapedevice ) output( *PRINT )

You could also output to *OUTFILE for some automation. *PRINT will give you something to look at. Blocksize and file length of each labeled item can be multiplied together to give you the best estimate of how much tape has been used, and therefore an estimate of how much might be added on.

I'm not clear on what you mean by "overwrite". Do you want to re-use the same tape the next night? or do you want to force your save to rewind back to the beginning if it reaches end-of-tape?

Tom
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by:KANEWONG
ID: 18825329
Yes, when I say "overwrite" means that the tape will be use again.  For example; the tape used on Monday will be used again on next Monday.
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by:tliotta
tliotta earned 250 total points
ID: 18827551
KANEWONG:

The common reasons a tape can't be reused --

1. It's been write-protected -- The lock on the cartridge has been switched by hand.

If so, simply unlock it before loading the cartridge.

2. There's an expiration date set on the tape label(s).

Expiration dates can be reset by the INZTAP command.  Initialize the tape when it's loaded, and set an appropriate expiration date during the save. Alternatively, use the CLEAR(*ALL) parameter for the SAVxxx command.

There are probably other possibilities, but those should cover almost all circumstances.

Tom
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