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Native and compression -

Created: 26 Feb 2013 | 4 comments

Our byte count to a DLT-S4 Tape is currently 665GB (native is 800GB and 16TB compressed) and we currently have Hardware compression enabled. I have with previous devices. such as SDLT600, experienced backup failures not much above their native capacity.

I would like to investigate if there is any way anticipate when the backups might start to fail due to native or compression restrictions but appreciate there is going to be data that is compressed on the fly (during backup) and also data that is pre-compressed which cannot be reduced in size any more.

I'm wondering if it is going to be a case of waiting for backups to fail or there is something I can do to preempt when Tape capacity is exhaused?

Thanks

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Sush...'s picture

Hello Marcopolo,

   There is no way to anticipate when the backups would start failing due to compression not happening and tapes getting full. The best practice is to use the tapes for the time period as mentioned by the Manufacturers (good for 1 year, 2 years... 7 years, 8 years).

Also its good to know how much data is getting backed up and accordingly to set the retention policy so that tape will get overwritten when the retention period has expired.

 

Thanks,

-Sush...

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pkh's picture

If you compress data which is already compressed, you are more likely to end up with more data than you have started with.  See my article on this topic

https://www-secure.symantec.com/connect/articles/c...

Although you cannot anticipate when your tapes are going to be full,  you can get an idea of how well you data compress if you switch to software compression and target a B2D folder.  Software and hardware compression will produce roughly the same compression ration with the same set of data.

The obvious way to prevent failure due to lack of tape capacity to to always have a spare scratch tape available in your library.

Marcopolo's picture

Thanks, we already pretty much do as suggested so I guess we just have to wait until a tape backup fails do to insufficient space.

Larry Fine's picture

If you are not able to achieve the native capacity of your tape drive you may have a hardware problem.  This technote only mentions LTO, but I would assume that it may apply to your DLT-S4 drive also.  I suggest working with your tape hardware vendor to test & diagnose.  With LTO drives, a clogged head usually produces no errors in BE or the standard diagnostic tools.

http://www.symantec.com/docs/TECH193200

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