Does Time Machine back up every hard drive in a Mac?

[Superman730]

Hi - I have a 2011 Mac Mini that I installed an SSD on a while back. When I did that, I kept the original hard drive in there as a storage drive. Does anyone know - If I set up Time Machine to run automatically, will it back up both drives or just the one the OS is installed on? (*I do time machine back ups to a Synology NAS with my other Macs)

 

[Brian33]

Time Machine can back up every drive directly-connected to the Mac. However, I think by default every drive other than the boot drive is automatically added to TM's exclusions. If you want the second drive backed up by TM you have to go to System Preferences-->Time Machine-->Options and remove the second drive from the list of excluded items.

I think this is the default because you probably don't want TM to back up every flash drive you insert!