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Append to media confusion

Created: 21 Sep 2010 • Updated: 23 Oct 2010 | 6 comments
This issue has been solved. See solution.

Hi all,

I have a question about what happens to appendable media when its full? Here's the scenario:
Backing up to a single tape drive ie. not a library
The daily backup job is configured to 'Append to media, overwrite if no appendable media is available'
The media set is configured to 'Overwrite protection period' - 1day & 'append period' - infinite allow append
There are 2 tapes allocated to the media set - after the job is done the tape ejects and the 2nd one is inserted ready for the next daily backup
So after some weeks the tapes will become full, what happens now?
It's my understanding that when the first tape becomes full the job will eject the tape and continue on the other tape, if that one is also full how does backup exec manage the tapes?
Will they start appending from the beginning of each tape appending from the most current backup data?
I'm sorry if i'm not making sense but as you can probably tell i'm a tad confused

Thanks

Comments 6 CommentsJump to latest comment

RahulG's picture

When you run an append Job the backup exec looks for the appendable tape in the media set where the backup Job is targeted to. Once the tape to which is appending is full ,It needs and overwriable tape to complete the backup Job . Depending upon the setting you have under tools --Options --Media management -- to overwrite recylable tape or scratch tape ..Backup exec will define if it has to write to a recycable media or sctrach medis(new tape).. If suppose the option is set to overwrite recyclable media 1st it will look for the recylable media and incase if it does not find it will prompt you for a new Tape ..

So the bottom line is Once the append writes to the tape and if its full the next tape which would be required to complete the job shuld be overwritable as it cannot be appended .

RahulG's picture

refer the following document  which gives the best description .

http://www.symantec.com/business/support/index?page=content&id=TECH5459

Larry Fine's picture

I am not exactly sure what you are trying to do, but I have a feeling it isn't doing it :)

Rahul is right.  When one tape fills up, BE will demand an overwritable tape.  If you only have two tapes, that really only gives you one choice as to what tape is going to get overwritten.  And if that tape has your full backup from yesterday, you probably don't want to overwrite it so quick.

Are your daily jobs a full backup?  or are the incrementals/differentials?

If you are running full backups every night, and they fit on one tape, then I suggest you avoid appending all together and simply use more than 2 tapes in your rotation and set the Overwrite protection to something like 4-5 days.

If you find this is a solution for the thread, please mark it as such.

azza00's picture

Thanks for your responses guys but it's not quite the answer i was looking for. I'd still like to know how backup exec handles appendable medai once it's full

So lets say i'm using a library where i have 5 tapes allocated to an appendable daily media set. Eventually they will all get full, how then are the tapes written to? They are now overwritable media as well. So the last tape in the media set fills up then what? I understand the theory that it searches for overwritable media which it will find but that tape is full, how is it written to? from the beginning overwriting all data along the way to the end of the tape?

pkh's picture

There are 2 parameters in the media set, OPP (Overwrite Protection Period) and AP (Append).  OPP is the period from the end of the job that last write to the tape to the time when it can be overwritten.  AP is the period from the end of the job that last write to the tape to the time when it cannot be appended to.

Let's say, in your case, you set both the OPP and AP to 5 days.  On day 1, your job fills up part of the tape 1.  It is now protected until day 6.  On day 2 your job fills up tape 1 and spans to tape 2.  Both these tapes are write protected until day 7.  On day 3, your yob fills up tape 2 and spans to tape 3.  Tape 2 and 3 are now protected until day 8 and so on.  The protection period for tape 1 remains as day 7.  On day 8, it becomes overwriteable and can be written to.

When BE writes to an overwriteable tape, it starts from the beginning of the tape and ALL the data that was previous on the tape is irretrievably gone.  If BE only fills up part of the tape, then the tape is appendable.  Otherwise, it is full and cannot be appended to.

BE does not care whether an overwriteable tape is full or partially full.  It will start from the beginning of the tape.

SOLUTION
azza00's picture

Thanks everybody, i am no longer confused  :)