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Tape usage - Size of Stored Data


Userlevel 2
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Hi,

Until recently, ~1 TB of data was stored on all our LTO4 tapes.

I recently changed 2 things:

  1. I created a Global Secondary Copy Policy
  2. I enabled software encryption for the (secondary) backups to tape (Re-encrypt, BlowFish, Key length 128, No Access)

Now, only ~750 GB of data is stored on all tapes before they are marked full. A decrease of 25%.

Is one of these two changes a known, proven and expectedcause for this decreased usage of the tapes?

Thanks!

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Best answer by iConsultant 17 May 2021, 09:26

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Userlevel 7
Badge +23

Hey @iConsultant !  To clarify, you created a new Secondary Copy or a new Global Dedupe Storage Policy?

I’m assuming you created a new Aux Copy (to tape) that copies the same data as your initial Aux Copy, but it takes up less space.  Is this accurate?

Few questions to understand better:

  • Where/how are you measuring the 1 TB vs. 750 GB? 
  • Are you adding up the unaged jobs on each copy, or are totaling the size of the tapes used?
  • Can you confirm that the jobs on each copy are the same?  Keep in mind, your previous Aux Copy may have different retention, as well as jobs that are aged, but on tapes.

Let’s start there and confirm we are comparing like to like.

Thanks!!

Userlevel 2
Badge +8

Hi,

I disabled the old secondary copies to tape and created new ones. The new secondary copies to tape are based on a Global Secondary Copy Policy (“umbrella” tape policy) and have Software Encryption enabled. The new secondary copies replace the old ones and copy the same data.

I compare the “Size of Stored Data”-column which shows up after selecting Exported Media (Library - Media by Location).

Btw I just notice that hardware compression is enabled on the new Data Path (apparently default), which wasn't enabled before. All primary copies use software compression. For the moment I will assume I need to disable hardware compression on the new Data Path.

Thanks for your response.

Userlevel 7
Badge +23

Compression could definitely be the factor.

Are the jobs on the new copy the same as the old copy?  Meaning are they an exact job-for-job duplicate, or is it just the same clients but newer backups?

I would say compression is the likely cause either way, just more so in the latter case.

Userlevel 7
Badge +23

Hi @iConsultant !  Hope all is well.

Have you had a chance to compare the jobs and the compression impact?

Userlevel 2
Badge +8

Hi Mike, I just checked after the weekend backups and unfortunately the size of stored data is still 750 GB. Disabling Hardware Compression on the Secondary Copy didn’t do the trick. Perhaps it's the combination of Software Compression and Deduplication on the Primary Copy and enabling Software Encryption on the Secondary Copy to tape. It doesn't cause an issue however, we just use a bit more tapes. If someone starts complaining I might advise using Hardware Encryption to see if that makes a difference, but for the moment I leave it as it is. Thanks!

Userlevel 7
Badge +23

Ok, please update this thread if you learn more.  I’ll mark your last reply as the Best Answer, though I can easily unmark it if needed.

Thanks!!

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