I'm booting up my iMac from an external SSD. It makes my computer run faster. How can I completely erase my iMac's internal HDD and use it as a storage device only?
iMac (21.5-inch, Late 2012), OS X El Capitan (10.11.5)
This is not a big issue, save one. Apple does not support this method as a permanent solution. However, you have a 2012 iMac. I have a 2012 Mac Mini. I used a 1 TB LaCie Rugged Thunderbolt HD to do this very thing through the Thunderbolt port. This worked great for a while. Personally speaking, I reverted back to my Primary Internal HD for OS X and the LaCie Thunderbolt as external storage. For reasons of Registration and so on. Internet Recovery, as well. I found no major difference in "booting speed" between the Internal or External HD. I upgraded RAM from 4 GB to the full 16 GB. and BAM!!
My Thunderbolt HD is partitioned as a Time Capsule(1st partition bootable) and Mac Storage(2nd partition). The choice is yours, of course.
Cheers!!
Disk Utility should do the job. You could reformat the entire internal drive if you want a clean slate. Naturally retaining a backup is recommended in case you ever have second thoughts about the deletion.
Boot from the external SSD and the open Disk Utility and do an erase of the internal HD.
Use iMac internal HDD for storage only.
