I have an old 2012 and am having SMART errors so it's upgrade time. I'm still on High Sierra. Indeed, I can't upgrade my internal drive to Mojave because of the SMART errors. I'm basically planning to do a clean install but, until I get everything set up, I'd like to be able to essentially run the system from an external SSD via USB 3. My thought is that I'll use Carbon Copy Cloner to create a clone of my internal drive. Then upgrade that to the most current version of Mohave. I'm assuming I can still boot from that drive on a 2019 iMac? That would make my life easier and let me relax a bit when getting everything installed and up and running. Any other tips here would be much appreciated. Thanks!
Got a tip for us?
Let us know
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Running Mojave from External SSD?
- Thread starter SkiHound2
- Start date
- Sort by reaction score
No need to boot a 2019 iMac with that drive. A 2019 iMac will come preloaded with Mojave. Just attach that external SSD to the new iMac and use Migration Assistant. Better yet, before creating an account on the new iMac, attach the external SSD and let MA migrate everything to the new iMac. I've done that very procedure each time I purchased a new Mac and it works well. However, do not create an account on the new iMac before using MA or you will have 2 accounts and that will make getting all your data in one place more difficult.
Yes, I don't intend to use the external ssd as my primary boot drive. I also don't want to use Migration Assistant to move everything every. I've been through a few computers and there is a lot of junk on my current drive that I don't want moved. And I think there are some issues caused by old conflicting software. So I want the ability to dual boot if I need some information from the old drive before I get everything set up the way I want on the new drive. I'm pretty sure the 2019 won't run on anything prior to Mojave.
You're correct in that a new 2019 iMac will likely not run anything prior to Mojave. You do realize that with the Migration Assistant that you do not have to migrate everything but can be selective. With your method you'll probably need to reinstall apps that can't be moved easily such as MS Office and some others. But if you have the time and don't mind a bit of extra effort, you should wind up with a nice new fast 2019 iMac. 
OP:
The new 2019 iMac may not boot up from the current Mojave 10.14.4 available for download from the App Store. It probably shipped with a special Mojave to support the new iMac & processors. This has happened with new Mac releases in the past.
Here is a thread from another 2019 iMac user that could not boot from the App Store 10.14.4:
https://forums.macrumors.com/threads/no-entry-sign-after-booting-from-usb.2176941/
The new iMac will be okay with the App Store 10.14.5 releasing the end of May or the beginning of June.
I would recommend getting your CCC clone done ASAP. You could always wait and install 10.14.5 on the clone later. BTW, if you have the resources it might be good to have 2 clones in case the Mojave install messes up one clone and the 2012 fails then you would have nothing.
"My thought is that I'll use Carbon Copy Cloner to create a clone of my internal drive. Then upgrade that to the most current version of Mohave. I'm assuming I can still boot from that drive on a 2019 iMac?"
The version of 10.14.4, the installer of which is downloadable from Apple, may not be "sufficiently new enough" to boot a 2019 iMac. I don't believe it will.
chscag has it right.
Yes, you can boot and run your current Mac from an external USB3 drive.
This is nothing more than a child's play.
So... I would suggest you do that with the Mac you have now -- if that's what you want.
When you get a NEW iMac, just connect the external boot drive and use "setup assistant" to "bring over" your stuff when you boot the new iMac for the very first time.
The version of 10.14.4, the installer of which is downloadable from Apple, may not be "sufficiently new enough" to boot a 2019 iMac. I don't believe it will.
chscag has it right.
Yes, you can boot and run your current Mac from an external USB3 drive.
This is nothing more than a child's play.
So... I would suggest you do that with the Mac you have now -- if that's what you want.
When you get a NEW iMac, just connect the external boot drive and use "setup assistant" to "bring over" your stuff when you boot the new iMac for the very first time.
The 2012 Mac mini was definitely only released with USB3. You will need an external USB3 drive and USB3 cable.
I thought from your first post, that you wanted to be able to boot the 2019 iMac with the CCC clone?
My thought was that I'd like to able to boot from the SSD if I needed information or files that were on the old computer, while I was getting the replacement set up. Sort of like booting into my current machine. But I'm getting an internal SSD and fully intend to use that as my main operating drive. So the booting from the external SSD would just be on an as needed basis till I get everything set up. I have some software conflicts (or something like that) on my old Mini and I don't want to just move everything onto the new system.
I'd bet a few pennies that a new iMac would take macOS at least back to Sierra. Also, I usually just do clean installs every couple years, but I understood that MA was all or nothing. ????You're correct in that a new 2019 iMac will likely not run anything prior to Mojave. You do realize that with the Migration Assistant that you do not have to migrate everything but can be selective. With your method you'll probably need to reinstall apps that can't be moved easily such as MS Office and some others. But if you have the time and don't mind a bit of extra effort, you should wind up with a nice new fast 2019 iMac.
I total agree with this - and not sure a "clean install" makes much difference
I did a clean install and upgrade of SSD ( 8 months ago) when I installed Mojave thinking it would be better to have a nice new clean SSD and fresh install - then I spent weeks going back to the "old drive / back up" for data and apps that i could have had migrated all in 1 shot
I've never had an issue with migration assistant in the past (not sure why i messed with it that time) - as long as MA is done right away and before setting up any accounts and users - Migration Assistant takes care of the "little things" like moving my Stickies Data base, archived outlook email from library folder, and other apps that store data in the "hidden" library and elsewhere. They can be a pain to get back to the former settings and with the same info. Also it is a pain for software like outlook / office - had to phone and get a new ID for Office - plus install the application software and even iWork apps that I like to have on hand like Pages 09 and iWeb had to be moved manuualy.
just throwing that out for thought
Also no need to update the back up drive - you can migrate direct from an older OS archive like Sierra to the new Mojave install
Yes, a clean install is a bit of a pain, but it gets rid of tons of stuff from your system drives that you may never need again. That's why I only do clean installs every third or fourth upgrade. I just do a screen copy of my old apps folder before upgrading. I have a password protected spreadsheet of all my software with key numbers, etc. Then after I do a clean install, I simply add the extra software individually. Since most of my power software is from Adobe, all I need to do is to log into your AdobeCC account and download your apps. This also gives me a chance to evaluate whether to reinstall the old software. I have never used the MA, or needed it. Getting rid of the leftover crap only needs to be done once a year or as needed. Otherwise, there's nothing easier than normal upgrading where it does the upgrading without creating a new account, as warned about on this thread earlier. I think the secret is to have at least two boot clones that you can experiment with, so you are never working on your original boot drives. I just make a bunch of clones with SuperDuper which only need 100GB if you don't store data on your boot. I just add a partition or two to the bottom of a spindle drive or an SSD, and I always have an identical clone in case of boot drive failure. Then I stagger the backups, so I always have an identical match or one that's close to clone back to the main boot drive. I have also found that it is easier to boot new OSs when they are new, as many of the heavy changes within that OS come later. I found this is especially true since Sierra.
Hi Edward,
There's no reason why it shouldn't be fine, or maybe I missed a post. I presume the external is acceptable because you have a slow spindle drive inside. That maxes out at around 150MB/s. USB3 gets a theoretical 500MB/s, but that's a joke, 200MB/s is more like its, so it's faster than your slow internal drive, but in today's world with Thunderbolt, is quite slow. Most SATA3 SSDs get around 550MB/s, so would be a lot faster inside where the drive bus is SATA3 (600MB/s) so 3x faster than running it from a USB port. But you can also do it with Thunderbolt which can (for Thunderbolt 1) speed up your external to its full speed. I would say that this TB connection will make your '13 iMac feel like new. I find this very important for the new OSs, since they are so large. You could also get a two SSD enclosure and pop in two SSDs with a TB connection. Then go to Disk Utility and put them in RAID0 with the Apple OS RAID. Then you may not be able to upgrade to Mojave due to the RAID, but you could just clone Mojave to it from your Mojave external USB. It would then work fine with Mojave and you could be getting around 1,000MB/s, that's 8x faster than you currently have. The new iMacs, after 2016, use the new drive type called NVMe and now get 3,000MB/s on a single unRaided drive (blade). I have a 2009 Mac Pro, and I use a NVMe blade (Samsung970EVO) which gets about 1500MB/s, but with a special card on my X16 PCIe slot, I get the full 3,000MB/s performance or within 10%.
Please let me add that I used to be in the business of making Macs (especially Mac Pros) as fast as possible so they can handle the rigors of still photo and video. Some of my scan files are in the 300MB range. If you do mostly simple stuff that everyone does, and aren't tackling large files, you probably don't need all the boot drive speed that I find essential.
Besides, now we have the iMac Pro, so all you need to do is shuck out $5,000 for the basic model... ;-)
If you have a fusion drive, I have some suggestions as well.
Neil