My internal hard drive on a Mac Mini is getting full. I plan to connect an external SSD to move my data to and leave the OS and applications on the internal HD. My question is how to address the external data so the applications know where to look for it and also make all new data go there.
iPad mini, iOS 12
Generally you do this yourself when you save a file via the File > Save As dialog. There is no way to force apps to save to a specific disk or location.
Some apps (for example, Photos, Music & TV) allow you to set the save location for their libraries and once you do that, all (photos, songs, video files) saved by them go to into their respective Library wherever it is located. You set this in Preferences for each of those apps.
Some apps save to locations that cannot be changed. Apple Mail & MS Outlook are examples. Their data is saved in ~/Library and cannot be changed, so it will remain on your internal HD.
Some apps allow you to set a default Save location. Look in Preferences for each app. Note, however, that even if there is a default save location for an app you can always save to a different location in the File > Save As dialog.
Generally you do this yourself when you save a file via the File > Save As dialog. There is no way to force apps to save to a specific disk or location.
Some apps (for example, Photos, Music & TV) allow you to set the save location for their libraries and once you do that, all (photos, songs, video files) saved by them go to into their respective Library wherever it is located. You set this in Preferences for each of those apps.
Some apps save to locations that cannot be changed. Apple Mail & MS Outlook are examples. Their data is saved in ~/Library and cannot be changed, so it will remain on your internal HD.
Some apps allow you to set a default Save location. Look in Preferences for each app. Note, however, that even if there is a default save location for an app you can always save to a different location in the File > Save As dialog.
Your Music and/or Photos libraries are normally the largest users of disk space.
Change where your music files are stored on Mac - Apple Support
Move your Photos library to save space on your Mac - Apple Support
Directing to data on external hard drive
