Tapes with jobs that have multiple retentions - what happens?

  • 23 August 2022
  • 2 replies

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I’ve been involved in backups for quite a while, but have mercifully been using drives ~ not tapes.  I’m now having to consider tapes.  

We have multiple SLAs, including:

  1. A monthly full backup to tape, retention to 62 days, lasts 1 month only
  2. A monthly full backup to tape, retention of 365 days - so 12 tape backups
  3.  A quarterly full backup to tape, retention of 365 days - so 4 tape backups

The last full backup of the month goes to tape.  So, I forsee a single tape (or a group of tapes with a mess of… ) consisting of 1 month + 12 month retention times.  Some of these tapes will have jobs that last a year as well as jobs that expired months earlier.  

What is everyone’s experience with such a thing?  We have over 750 servers involved here.  CV has but one tape drive currently and an operations group to rotate tapes.  


Thank you in advance for any experience you can lend me… 


Mike Rucker


Best answer by Jos Meijer 23 August 2022, 23:22

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Userlevel 7
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As your SLA line-up contains multiple monthly full requirements I am assuming we are talking about multiple storage policies?

Do you intend to allocate each storage policy on it's own tape set or everything on one big tape set?

Based on the topic subject I assume the latter. In this case the tape will be returned to the scratch pool after all jobs are aged. If this assumption is correct, I would not allocate big data apps backups on this tape as it will keep your tape in use and prevent it from being returned to the scratch pool unless you perform manual corrections.

Also 750 servers, seems to much for one drive, but how much data do you need to actually transfer to tape?
Can you also inform us what type of tape and drive you are using? LTO8 for example?

If there are large amounts of data to copy to tape, depending on your business requirements you might be better off by using a worm disk based solution on an off-site location. A lot of data can cause a lot (really a lot) of tapes to be written.

Userlevel 3
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A Jos indicates, dedicated tape sets can be used for this but often a single tape set is used for performance/cost efficiency reasons.

The challenge with the single tape set is that the individual jobs will pass their retention dates but the media will be kept until every job on the tape has aged.  In effect this means the earlier  jobs will be retained until the last job on the tape is aged out. You will end up with a lot of partially used tapes.


You can mitigate this with “Media Refresh”

It’s a balancing act but a combination of ‘months after the media were written’ and ‘% or less of media capacity is used’ thresholds can potentially reduce the wasted space on media.