Estimating How Long Tape to Disk Auxcopy will take

  • 30 August 2022
  • 2 replies

Userlevel 1
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I am in the process of moving all our data from tape to a disk library and need to estimate how long this will take. Has anyone come up with a reasonably accurate way of predicting how long Aux copying data for a given copy would take.

I have 6 x Tape Drives in a library. This has been used a a target for multiple Auxcopy operations for multiple Storage Policies. Due to tape contention a multiplexed multi stream Auxcopy for a Storage Policy copy could be written to 1 to 4 drives depending on drive availability.


I am also interested to know how this works. When the operation began it copied the oldest data first , but as time went on the completed and partially copied data began to appear throughout the timeline. Is there away to make the most recent data copy first?


Does an Auxcopy operation begin copying all jobs on a given mounted piece of media, or does it only copy some jobs and will have to mount that tape later.



Best answer by Jordan 30 August 2022, 06:13

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Userlevel 5
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Time will depend on too many factors to really be able to calculate however you can approximately estimate it by letting it run for some time and see how much progress (TB copied out of total TB to be copied) was achieve and then scaling that out. 


With multiplexed data, aux copy will need to seek a lot more on tape than during the original write see it needs to process data based on job and not based on media or even position on media. So you will see the same tape potentially be mounted/unmounted many times as the aux copy job processes the list of jobs to be copied.


Userlevel 7
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@DaveK as @Jordan already stated it's very hard to predict this besides streaming there are also factors that come into play like disk write latency, especially when the amount of drives that you use start to increase. you could run a test drive to see what figures you are going to get that at least gives you some idea what kind of recovery performance you could get. 

also keep in mind that in case this is a production system that during this auxcopy both backup and recovery speeds are most likely also going to get affected.