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macrumors newbie
Original poster
Apr 6, 2019
Hi All

I have just bought a new 2019 iMac. I have an internal fusion drive. I bought a Samsung X5 SSD external drive. I wanted to install a copy of mojave on this and use this as a second bootable drive and place my graphics programs like After Effects and Premiere on it. I couldn't get it to work?
I erased the SSD (format Mac OS Extended (Journaled)).
I then turned off iMac and turned back on holding down the option key, hoping to see the SSD drive in start up mode but the drive does not appear.
Does anyone know what i'm doing wrong or can the Samsung X5 SSD not be used as a bootable drive?



macrumors newbie
Apr 4, 2019
Sacramento, CA
The reason it is not coming up is because it is blank, no OS installed.

Boot into recovery, click Install Mojave. When it gets to the drive selection, the SSD should come up as an option.
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macrumors newbie
Original poster
Apr 6, 2019
Thanks bondavi this eventually worked. The other problem I ran into was in disk utility the default selection in mojave OS is volume only, so when i was erasing the hard drive I was really only effecting the volume and not the whole hard drive, you need to select in views (top left hand corner) Show all devices, then you can select GUID Partition Map when erasing the SSD disk.


macrumors 68030
Jan 19, 2015
Oregon, USA
The Samsung X5 can be used as a bootable drive, but it will not show in the startup manager until a bootable macOS is installed on it.


macrumors Penryn
Feb 20, 2009
mike wrote:
"Unless this has changed in Mojave, you won't be able to see your iMac when booted from the external. Reformat APFS like your iMac."

Are you sure about this, Mike?

I have reformatted the INTERNAL drive on my 2018 (t2-equipped) Mini to HFS+, and it "sees everything" that I attach to it.

No APFS in this house!
(well, I DO keep an APFS formatted drive around which I will use to upgrade to the final version of Mojave when it's available, but that's the drive's only purpose. I don't use it for "regular things". This 2018 Mini will remain "forever HFS+"...)
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