Which Devices Should You Boot Your M1 Mac From?
Before going any further, allow me to reiterate: unless you’ve got a compelling reason, only ever boot your M1 Mac from its internal SSD. That’s how it’s designed to work, and that’s how it works best, even when it’s not working properly.
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The best reasons that I know for wanting to boot an M1 Mac from an external disk are when you need to be able to run several different versions of macOS, perhaps for testing purposes.
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One last warning: don’t try cloning its internal SSD to an external disk ‘so that you can boot from that’. Sometimes you can get away with it, but the best way to install macOS on any bootable external disk is using its installer app, and not cloning.
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If you want to use your M1 Mac when it’s booted from an external disk, aim for a Thunderbolt 3 device returning at least 1 GB/s read and write speed, faster if possible.
Around Mavericks or so, macOS started to perform much worse when booted from a spinning hard drive. (This was compared with earlier versions using the same hardware—obviously, adding an SSD made it perform better than before.)
Now, you can definitely tell when you’re using a slower SSD, even though it has at least double the throughput of a hard drive—and much better latency.
Before, I think the difference was that macOS started trying to do more things at once, which played to the hard drive’s weaknesses. Now, I think we’re seeing a different effect, which is that SSDs have gotten a lot faster and macOS is able to take advantage of that. (To a point—even with my new MacBook Pro’s fast SSD I can feel when the system is paging because Downcast or systemstats is using 25 GB of RAM.)
Previously:
- How Recovery Works on M1 Series Macs
- Booting an M1 Mac From an External Disk With Monterey
- The Role of Bootable Duplicates in a Modern Backup Strategy
- Poor Mac Performance Without an SSD
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Slight typo:
Now, you can definitely tell when you’re using a slower SSD, even though it has at least double the throughput of a hard drive—and much batter latency.
Should be better latency. Batter latency is the time between when a pie is launched at your face it hits...
I used to use external drives with a "known-good" OS troubleshooting a lot in the big cat days. But as you say it got crazy slow, enough to be almost useless. Recovery solved some of it, but overall it has meant I end up doing more semi-blind clean installs rather than trying to fix a wonky OS.
Poor support for booting from external drives is one of the many things I dislike about these new macs. Macs used to be *the best* for booting from external drives, far better than Windows and Linux and any of their associated bootloaders, be they BIOS-based or UEFI-based. It was simple to do and it worked very consistently and reliably. And there were a ton of good reasons to boot from external drives, from needing test macOS installations to being able to create bootable clones of your internal disk so that, should your internal disk, die, you can get right back to work within minutes.
There's no reason it still can't be like that, but Apple is obsessed with control and security theater now, and so we all lose out, the platform degrades, and with it the ceiling of quality in the entire computer industry sinks with it.
Also useful is the possibility yo boot different Macs from the same external SSD, when you work at different sites. and want to carry just the SSD in your pocket. That is possible with Intel x86 Macs, but can be problematic or impossible with Apple silicon ones. Apple should fix it.
