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Need to understand the attached snapshot (overwrite & append period)

Created: 09 Feb 2014 • Updated: 10 Feb 2014 | 7 comments
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Dear Experts,

Please see attached screen shot for properties of 'daily_media set', it says 'overwrite period as 6 days' and for append period 'none, infinite allowed'. This cartridge is of 2.4TB after compression and takes daily differential backups of our servers.

Now from the screen shot, my understanding is the bexec will continue to append until the end of tape is reached and when no space is available to append it will start again from beginning of tape. But this makes any sense to cotinue append? when the overwrite protection is set to 6 days from which I understand that any differential backup on tape will expire after 6 days whether you overwrite or not, is this correct ?

So, I was thinking to change the append period from infinited allowed to 6 days so, it append for 6 days and then again starts from beginning of tape, this makes sense ?

I know the above are easy, but I am in process of understanding this procedure.


Operating Systems:

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pkh's picture

When you reach the end of the tape, BE will require an overwritable tape for the job to continue. It cannot wrote to the front of the tape.

With your setting, the tape would be protected for 6 days after the last job has written to the tape. Whatever backup sets that are on the tape would remain on the tape until the tape is overwritten, even if the overwriting takes place one year later

wajeeh_r's picture

Hello Pkh,

So what you are saying in my case until end of tape is reached with the last job written, ONLY then the 6 days protection counter will start ? and after 6 days are finished BE will over write the same tape from front ?

Is this right way ? OR I need to do adjustment on this ?

pkh's picture

It don't have to be the end of the tape. After the last job wrote to the tape, the OPP will start. This can be the middle of the tape.

When the OPP is over, the tape can be overwritten. It may not happen immediately. The tape will only be overwritten when it is next used

P.Dusome's picture

The real answer is, it depends.

The default storage usage setting for a job is:

"Append to media, overwrite if no appendable media is available"

With the above job setting, in your case the media would never be overwritten.  If you want the tape to be overwritten, it would have to be in a job where the storage use is:

"Overwrite Media"

If you want the tape to be overwritten because it is more tha six days old, set the append period for 5 days, and don't use the tape again for a week because...

The timer restarts every time you use the tape.

pkh's picture

"Append to media, overwrite if no appendable media is available"

With the above job setting, in your case the media would never be overwritten.

No.  This is not true.  If the job cannot find an appendable media, then it will find an overwritable media to overwrite.

P.Dusome's picture

The media is set to "Infinite - Allow append." Ergo, the job will always find appendable media.

pkh's picture

Yes, but for the second and subsequent tapes, BE will only overwrite tapes, so his tapes will still be overwritten