How full is my backup tape?

40 pts.
Tags:
AS/400 backup
IBM i
System i
Tape backup
V4R3
Is there a way on the AS/400 (ours is at V4R3 so I still call it that), to tell the percent used of a backup tape?

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Hi,

Do you use/have BRMS? I believe in BRMS there are reports available for this sort of information. If you don’t have BRMS then you may be able to work it out from the data from a DSPTAP output, using the number of blocks/records already used and the total number of blocks/records (but I’m not sure if the DSPTAP will tell you the total number of blocks/records).

Regards,

Martin Gilbert.

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  • TomLiotta
    Determining how full a tape is is like wondering how many rocks it will take to fill a hole after some rocks have already been put in. How big is the hole? The size may change while rocks are being put in. weak sections may collapse (i.e., be marked as unusable). How big were the rocks so far? Rocks come in a lot of sizes. You can pack a very large number of tiny rocks in, but each one may have a little bit of space between it and the next one. The wasted space adds up for a million tiny rocks differently than if just one very large rock was put in. How big are the rocks you still want to put in? If your rocks will have a lot of wasted space between a large number of them, the the remaining space will be used faster. Maybe only one big rock will fit. What kind of tape/drive is in use? More recent and more intelligent tapes/drives have digital logic that helps with positioning. Inter-block and inter-file gaps can be very different with different tapes/drives. Wasted space can be significantly different. What compression and/or compaction was used and will be used? Is software compression going to be used? Hardware compression? Hardware compaction? Rocks may be jostled to cause them to settle into more compact spaces. Careful placement of each rock may make much more efficient use of the space. If the hole collapses near the top, it might fill itself. The remainder of the tape might be unusable. How do you count such a percentage? Tape usage has a lot of variables. Tapes themselves can be individually variable as they are used. For the most part, you learn by experience. You use particular kinds and qualities of tapes in a mostly predictable environment, and you track usage. The tracks you create guide your future. Tom
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  • Davidmichel
    Just to add to the above. It is up to the application to query the tape drive for the remaining capacity. However tape drives base remaining capacity off the native (non-compressed) capaicity of the tape. So if you are doing backups without compression and have a 400gb tape and the drive reports remaining capacity of 200gb then you know there is 200gb remaining. When compression is used the tape drive is still basing its caculations for remaining capacity off the native capacity. So it could report 200gb remaining space on tape and then proceed to backup another 300gb to the 400gb tape because with compression it now fit 500gb to the tape. Also reported compression ratios are just one step up from useless. Typically a 400gb drive will be reported to fit 800gb compressed on the tape. Yet the compression ratio really depends upon the data being backed up. Some data such as jpg, mp3, zip, and many others are already compressed and so you can expect no further compression, and hense the tape will still fill at 400gb. Bottom line the way to tell is to backup until the tape is full and then see how much data fit. This will give you a baseline to work from. So for example the tape filled after writing 800gb to tape. Then in the future when backing up the same data you will have a good idea of the remaining space on tape.
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