Call me old school, but I don’t trust all my digital data to reside solely in “the cloud” (that would be iCloud for we Apple fans). That’s why I use iTunes Match and iCloud, yet also have my music library on an external hard drive connected to my iMac.
iTunes Match is a service that stores all your music in iCloud—even songs imported from CDs or not purchased in the iTunes Store—and makes it available on up to 10 of your devices and computers. With iTunes Match — which costs US$25 annually— you have access to your complete iTunes music library at any time. If you have this service, you can download all your music to your Mac with these steps.
If you have multiple Macs, pick one you wish to store your music library on.
Open iTunes and make sure iCloud Music Library is enabled in iTunes > Preferences > General.
Choose Music from the dropdown menu, and select the Library tab.
Go to View > Show View Options.
Click on the checkboxes next to iCloud Download.
Songs that aren’t already stored locally on your Mac will be designed by a cloud with a downward arrow. You can download tracks one-by-one by clicking on the cloud icon, or by selecting multiple songs and control-clicking on them, then selecting Download. Once all the songs/albums are on your Mac, take the further precaution of backing ‘em up to a second disk drive.