Explanation of primary and secondary density when defining a media type

General Discussion
1

Hello,

When adding a mediatype to CTA, I see the options for --primarydensitycode and --secondarydensitycode. I can’t readily determine what function this option serves in CTA based on the source, and they’re not a required option.

While trying to work out what this mean, I went down a rabbit hole of calculation that seemed to match the numbers listed in the CI deployment, however I’m finding correlation rather than confirmation. What is the significance of these two options?

Additionally, I see --nbwraps as an additional option, and I can guess this might have something to with RAO. Are you able to explain the significance of this, and does it match the relevant tape specification (28 for LTO-7)?

2

This page in the documentation explains the media types. There are several linked GitLab tickets which explain the density codes.

--nbwraps is indeed for RAO for LTO media. LTO-8 12TB has 208 physical wraps. I believe LTO-7M has 168 wraps. We don’t have any LTO-7 drives so I don’t know the number of wraps for LTO-7 tapes off the top of my head. For the moment it does not matter as this feature is not yet implemented in CTA (but will be soon).