Nas media files to Ext HDD

Time machine can ADD an Additional drive at any time. Time machine will start new backup as of this moment, and make a full backup at low proirity in the background.

when completed, every-other backup will go to every-other Working drive. Each drive is a stand-alone backup set. and either can be removed, set aside, or Erased at any time.

do not anguish over how to accomplish this. Just set time machine to work on that 6 GB drive and before you know it you will have a full backup of everything you care about and maybe a few incremental backups as well.

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Time machine will copy all files for all Users on all drives DIRECTLY connected to your Mac. If all the media files you are concerned about are currently on a NAS, you may need a different solution to make a duplicate of the NAS.

Let readers know and we can think about this differently, if needed.

Time machine really does not want to back up drives that are not MacOS formats, or drives that are not local, because those kinds of drives can not compute the data structures used to make Time machine backups proceed simply in the background.

Drag and drop large globs of files with Finder can Create a second copy, but there is no automated way to Update that copy when changes are made to the originals.

Solutions like CarbonCopyCloner, SuperDuper! and ChronoSync will likely be more useful. Any of those can create a backup, then update the backup with files that are found to be modified later. In most cases, the original backup and the updates can not proceed at low priority in the background without some impact on your foreground work. You can always start them at the end of the day and let them run into the night.

Readers here have chosen CarbonCopyCloner often, and rate that software highly, and its author as extremely helpful. The others are not too far behind. All these packages have modest costs, and a certain amount of learning curve to use them to their fullest. But you can make your first backup starting in a few minutes with any of them. Not quite a simple as Time machine, but not too bad.

If that did not answeer your questions, please ask again.