I just purchased a SanDisk extreme 510 480GB portable SSD. I sm successfully using this as a boot drive (start-up disk) on my late 2012 Mac Mini i5 2.5GHz/16GB RAM and Intel HD Graphics 4000. 500GB hard disk and 4TB external USB3 back-up disk.
The improvement in speed to start-up and program loading has been impressive:
Using the internal HD drive: on to desktop took 2 minutes 48 seconds
Using SanDisk 510 external with USB3: on to desktop took 42 seconds that is exactly 4 times faster
By comparison my MacBook Air 2015 i7 500GB internal SSD and 8MB RAM started in 28 seconds from on to desktop. Both are running OSX High Sierra. I will keep my MacMini for another year or so! The impact on productivity is noticeable.
NOTE: when formatting the SanDisk with th MacOS Disk Utility do not forget to select “Show All Devices” in the “View” menu on the Disk Utility toolbar on the left. Then select “Erase” in the middle of the toolbar and check SanDisk Ext SSD snd then enter your new disk name (i.e: MyMac2. Make sure you select as Format:
Mac OS Extended (Journaled)
GUID Partition Map
Click on the “Erase” button and the disk willbe formated. You can now download High Sierra to this disk and use it as a start-up.
If you have any useful data on your SanDisk back it up first.