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on an M1, can a 2.5" SSD serve as an external boot drive?

It has become clear that the only way to create an external boot drive for an M1 involves using Thunderbolt-3 equipment. Is it possible to use a 2.5" SSD for the purpose, or must it be an NVME SSD?

Mac mini 2018 or later

Posted on Apr 18, 2022 6:35 AM

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Posted on Apr 18, 2022 8:13 AM

Some seem to work with the SSD in an USB-C enclosure and some even with USB-A enclosure. Which ones work seem to not be determined.

Boot from external disk on M1 Mac - Apple Community

However, this was for HBig Sur and may not be applicable to Monterey.

15 replies

Apr 19, 2022 7:28 AM in response to Birck Cox

Birck Cox wrote:

You mean that, no matter how fast the external drive is by itself, the combination of basic speed, cable type and length, and enclosure type will reduce overall speed-when the external drive is running the system- to well below the speed achievable with an internal drive(?).

Exactly.

For the sake of having the external drive, I can live with that.

But it's not about you. Macs are very expensive. When most people hand over that much money, they want to get every drop of performance that they are paying for. Those are Apple's customers and that's what they value. If you have different values, then perhaps you've chosen the wrong product.

For example, considering the problems some people are having with Monterey

You will find virtually identical reports for every single version of macOS, going back to version 1.0. If this is the basis of your concerns, then again, you've chosen the wrong product.

I wouldn't mind having an external version of Big Sur on hand, if only for purposes of comparison. So the faster I can make the components in the external chain, the better-?

Then I can save you a lot of time and effort on those comparisons. Your external version of Big Sur will run from 50-90% slower on your external hard drive.


Regardless, you don't need an external drive for this. You can install multiple version of macOS on the internal drive. See instructions from Apple here: Installing macOS on a separate APFS volume - Apple Support


Note that these instructions are designed strictly for beta testers. There are lots of unmentioned assumptions about how to use the system in this configuration. If you don't already know the risks, you are playing with fire.

Apr 18, 2022 9:48 AM in response to lllaass

Your reply confirms what I have read elsewhere. The only combination that seems sure to work is an all-Thunderbolt-3 chain, ending in an NVME SSD. A reliable source told me he was using a Samsung 2.5" SSD via USB-C. Others have said SSD-Thunderbolt 3 cable to thunderbolt port works; Many of them report "Works sometimes, but not always". Anyway, it looks as if I'm going to need Thunderbolt equipment if I want a reliable external boot drive. And I'm dropping back to Big Sur. Some have suggested that Monterey is part of the problem, and I can always re-upgrade to Monterey. Apple, of course, admits nothing, and when I bring the subject up with AppleCare, they respond by asking me why I would want an external boot drive in the first place. The fact that a choice of Startup Discs has been a feature of the Mac preferences for 30 years or more doesn't seem to matter to them.

Apr 18, 2022 10:47 AM in response to Birck Cox

I have both and NVME TB drive and also a USB 3.2 gen 2 drive. While both can boot my M1 (12.3) Monterey Mac the TB drive is the most consistent That being said the value of a bootable drive that was so nice with an Intel Mac. is not the same with the M1 Macs. There was a time when your internal drive failed you could just use the external drive. You can no longer do this with M1 machines as it requires a working internal to boot from the external. So that feature is now gone.

Apr 18, 2022 11:15 AM in response to tbirdvet

Good grief! That was at least half the value of keeping an external boot drive connected. And it will probably compromise my system as well-I want to have an alternate OS, like Big Sur or Catalina, on hand. What's going to happen when I try to boot into Big Sur from an internal Monterey drive? Can I expect compatibility? Not to mention what we are supposed to do if there IS an internal disc failure-try to "Recover" a failed internal disc? Then rebuild the failed disc via Time Machine? This is hopeless. But thanks for the bad news.

Apr 18, 2022 2:22 PM in response to Birck Cox

I have a 4-bay Thunderbolt 2 enclosure for 2 1/2" SSDs, which I used to use for my 2013 Map Pro. I now have it connected to my Studio Max via TB2>TB4 adopter.


I just installed 12.3.1 on one of the 2 1/2" SSDs in the enclosure. It installed and booted fine and I migrated my Studio ™ backup to the that drive. It works fine but is sure slower, especially starting up. The SSD is an EVO 840 500GB SSD.

Apr 18, 2022 4:21 PM in response to Birck Cox

New internal SSD type of drives will usually be faster by design than external drives. In previous years one could use an external SSD and it would be faster then an internal mechanical drive but since all the new Macs have internal SSD's it is no longer valid. I can match my internal drive speeds on my MBA M1and Mini M1 with an external NVME in a TB enclosure assuming I use the correct NVME drive (not all are the same speed). Not sure I could do that with the new Studio Mac's because they have even faster drives than previous Mac's.

Apr 18, 2022 5:28 PM in response to Birck Cox

Birck Cox wrote:

Well, that is new information. First time it's come up. Why would that happen?

Because the internal SSD is faster than any external drive. I don't know what else I could add to tbirdvet's response. In theory, the Thunderbolt bus can support that speed. There are some 3rd party M.2 SSDs that are equivalent, but those are also designed for internal storage. Your bottleneck will be the enclosure. The fastest enclosure I've seen is 2800 MB/s, which is a little less than half the speed of the Studio Mac's internal SSD.

Apr 19, 2022 4:59 AM in response to etresoft

Ah. You mean that, no matter how fast the external drive is by itself, the combination of basic speed, cable type and length, and enclosure type will reduce overall speed-when the external drive is running the system- to well below the speed achievable with an internal drive(?). For the sake of having the external drive, I can live with that. For example, considering the problems some people are having with Monterey, I wouldn't mind having an external version of Big Sur on hand, if only for purposes of comparison. So the faster I can make the components in the external chain, the better-?

Apr 19, 2022 1:43 PM in response to etresoft

Birck Cox wrote:

You mean that, no matter how fast the external drive is by itself, the combination of basic speed, cable type and length, and enclosure type will reduce overall speed-when the external drive is running the system- to well below the speed achievable with an internal drive(?).


Exactly.

For the sake of having the external drive, I can live with that.

But it's not about you.

Well, It's about me as far as my remarks in this conversation are concerned.


Macs are very expensive.

Yes, and?


When most people hand over that much money, they want to get every drop of performance that they are paying for.

That may be true for "most people", whatever that means; not necessarily for me.


Those are Apple's customers

So my lack of fervor for Speed At All Costs makes me NOT one of Apple's customers? Allow me to point out that I've been using Macs since the early 1990's, and buying them since the late 1990's.


and that's what they value. If you have different values, then perhaps you've chosen the wrong product.

"chosen the wrong product"? Frankly, I find the pathological nature of your condescension appalling



Apr 19, 2022 2:26 PM in response to Birck Cox

Birck Cox wrote:

So my lack of fervor for Speed At All Costs makes me NOT one of Apple's customers?

"chosen the wrong product"? Frankly, I find the pathological nature of your condescension appalling

So you transfer your animosity from Apple to me?


All I’m trying to do is help you get the best possible user experience. There’s no way to sugarcoat it - that means using the most recent operating system, and only that operating system, on the internal drive. It’s not 1999 anymore.


Are you sincerely asking for help to find a sub-standard user experience? You want to fight Apple with each OS upgrade? You wan to endure bug after bug because Apple has zero interest in supporting your custom configuration? You want Apple to turn back the clock a quarter century? That’s simply not going to happen.


You have to decide how you want to move forward. There is no going back.

Apr 19, 2022 2:46 PM in response to Birck Cox

This may help. Even though you can buy an NVME drive that has very fast speeds the external enclosure cannot support those speeds due to architecture and heat (as temp goes up it throttles down). I have several NVME drives in different enclosures. My M1 Mac Mini shows a r/w speed of 3000/2850. My external WD SN750 drive has a spec of 3400+ but I can only achieve speeds of 2580/2400 in a Trebleet or Acasis TB enclosure. If I was to get an NVME drive such as a WD SN850 (speed ~7000) I still could not achieve a faster external speed. In other words I have maxed out.

Apr 25, 2022 4:08 AM in response to lllaass

My issue is Audio drivers / deep security -preventing full system back up to be usable.

thunderbolt m2-ssd does boot. (12.3.1)

ability to use what does work from internal drive specifically Avid and or MOTU

tried 2.5 evo via TB to esata. Boots but cant use signed drivers (will not load)

followed lowered security guidelines,

thank you everyone for chiming in.

on an M1, can a 2.5" SSD serve as an external boot drive?

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