Dear Friend,

When you run a pool, it only uses the limitation you submited for that pool and is not aware of other pool's limitations. So if you ordered the "Indexes" pool to use only one specific drive, it uses only that drive and it has nothing to do with other pools. When other pools run, they look at their own sibmitted limitations and since they are allowed to use that specific drive you used in "Indexes" pool, they will use it for backup because they are allowed to do so.
To do what you want, first limt your "Indexes" pool to use that specific drive, second force other pools not to use that drive by selecting other drives on all pool's configuration, this must be done on all pools that you don't want to use that specific drive.
This action doesn't seem optimal, because you only need a few minutes per days for index backups and you waste one drive for a few minutes per day!!

Thanks for your suggestions.
I was thinking to do the same, but wanted to see what's the best practise.

You did check admin guide and chapter called "Directing client file indexes and bootstrap to a separate media pool"? What I would suggest is to have such pool on disk and then have them staged later to tape and cloned as well (especially if using some of the latest media types).

Thank you for this info.