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Byte Count vs Tape Capacity

Not applicable

Backup Exec 2010 R3 Service Pack 4 - Small Business Server Suite  (Media Server Version 13.0 Rev 5204 (32-bit).  Administration Consol Version 13.0 Rev 5204.1270 (32-bit) Desktop and Laptop Option Version 3.1 Rev 3.46.06a.  FIPS version - not enabled.

Server 2003 with a Quantum Ultrium 3 deck.

I'm trying to figure out why a client's backup job has stopped completing succesfully.  The size of the back up has grown steadily in the last few months mostly due to Exchange growth and the number of Quickbook backups they are keeping.  The jobs are failing indicating the backup window has expired.  The jobs typically complete in 2hrs, the windows is 6hrs.  After troubleshooting I find that the tapes are full.  I have done the following since making this determination.

- Checked overwrite and apend settings.  For purposes of trying to get successful backup I have set overwrite protection to none and apend to infinite.  The job is set to use hardware compression if available otherwise software.

- Did a quick erase, verified the tape was 'blank' and put the tape back into the correct media set.

- Ran a successful test job that shows the total byte count of 201,976,547,800 bytes or about 188GB. It further shows an Online overwrite capacity of 400,308.00MB or about 390GB which is what the physical tape shows under Devices. 

- I went through and deleted about 40GB of data to reduce the size of the backup job.

Ok.  So I ran a job last night.  The result - it failed.  I assume it was waiting for a second tape.  The tape is now full showing used capacity is 389.7 GB of 390.9 GB available.  Ok. The tape is full.  However, byte count in the job monitor is showing a byte count of 183,392,700,450 bytes or about 170GB.   In my job history I have successful jobs on a single tape that were 246,688,635,872 bytes or about 229GB.  

So I expect with compression to have the ability to backup ~300GB of data.  Yet my blank tape is full at 390GB but I have a byte count of 170GB.   I know I'm missing something here but I can't figure it out - never had a BE problem in 15 years that I couldn't figure out myself.  I'm open to any suggestions.  Thanks.



Level 6

An LTO3 has a native capacity of about 400GB.  But if your tape is showing in BE as "media full" and you only wrote about 200 GB, I suspect that you have a clogged tape head.

This may help:

Tapes report full before their Native Capacity is reached

   VIP    Certified

 I have set overwrite protection to none

I hope you have not set the Overwrite Protection Level to None because this means that there is no protection for your media and all your OPP and AP does not apply.  You should always set your OPL to either Partial or Full.


Another possibility is that your source data contains a lot of data which is already compressed, like zipped files, movies, sound clips and pictures.  When you compress data which is already compressed you can end up with more data than you start with.  As a test, turn off compression and see what you get.

Level 2

Hi Larry,

Thanks for the reply.  We are able to get smaller jobs to be successful, but the existing job spans two tapes if we let it.  Even though we have gotten total backup size down to 100G, or a quarter of its native capacity.  Therefore I agree with the assesment of a clogged tape head.  We have cleaned the drive 4x with no success.  We have tried new media and old media.  The drive is generic (Quantum mechanism) so no ability to get support from vendor.   The drive is old so I am going to assume the tape head is damaged beyond repair.  I'm going to recommend my customer buy a new drive or move backups to the cloud.  Thanks for the input.

Level 2

I prefer Overwrite Protection Level be at None.  My clients rotate and store tapes so even if a tape was overwritten and the data lost, they have plenty of other sets of the same data.  They and I are aware of the risks.

We did run a job with compression off - it did not resolve the problem.  Most of the data tha is being backed up was not compressed to begin with.

Thank you for your input.  I believe the poster above who suggested a clogged tape head is correct after reading and following his recommended article I've come to the conclusion that the tape deck may be damaged.

Employee Accredited Certified

Did you set you jobs to start as overwrite. Append infinite with jobs set to start as append will add data to a tape and if the tape is already part used you are then more likely to fill the remaining space which will then result in BE asking for another tape to use and the job eventually timing out (depending on your settings)

Level 6

I believe that a Quantum LTO3 drive would still be supported by Quantrum, but you are correct in that if it is out of warranty or a support contract it may be most cost effiective to simply replace it.