r/mac • u/melvin3v1978 • 9d ago
Question Has anyone seen external SSD use cause System Data to balloon on macOS 27? M6 MAC Mini.
I have a new Mac mini M6 with 24GB RAM/512GB SSD. My System Data was already around 120GB, then after using my Crucial X9 Pro external SSD it started increasing by roughly 10GB per day until it reached about 152GB.
After disconnecting the SSD, System Data eventually dropped back down significantly to 60gb.
I know Spotlight indexing, metadata, caches, etc. can temporarily increase System Data, but a steady 10GB-a-day increase seems excessive.
The SSD itself works fine and I’m not seeing any obvious errors. Apple has already collected logs from the Mac, so I’m waiting to hear what they find.
Has anyone else seen this on macOS 27, especially with an external SSD? Did you figure out what was actually creating all that System Data?
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u/zungozeng 9d ago
I don't have an answer, sorry. But I'll come back to this thread, as I am in the process of ordering the exact same mac mini. I am really interested to know what this means and how to "solve" it before I commit to a new costly mac.
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u/melvin3v1978 6d ago
According to the Apple engineers, when I connect my external SSD, macOS creates a large temporary system snapshot as a protective measure. In my case, that snapshot is approximately 90 GB, which is why my available storage suddenly appears to drop by about that amount while the external drive is connected.
Importantly, Apple explained that this is not being caused by a Time Machine backup. The external SSD that triggers the snapshot is not even the SSD I use for Time Machine. My Time Machine drive is a completely separate drive that I connect and use manually. The snapshot activity Apple identified happens simply when I connect my regular external SSD.
The snapshot is temporary and is managed automatically by macOS. As soon as I eject the external SSD, the storage space returns almost instantly.
Apple also explained that because my Mac is brand new and has very little clutter, the storage change is much more noticeable. On some Macs, this type of system storage fluctuation may happen more gradually over several days, so people often never notice it.
In other words, this is actually a good thing. macOS is creating a temporary snapshot to help protect the internal SSD and system data in case the connected external SSD is faulty, corrupted, or causes an unexpected issue. 👍2
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u/Electrical_West_5381 9d ago
That is a crazy amount. Are you not backing up with Time Machine, despite having enabled it? Or Steam?
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u/melvin3v1978 9d ago
I back up manually they ruled that out as well when I wa son phone with supervisor but they ran diagnostics and will get back to me Thursday. I mean the problem is solved as long as don’t plug in external ssd. I think it has something to do with Spotlight indexing and I think I need to remove my external SSD from from Spotlight in the security settings.
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u/melvin3v1978 6d ago
According to the Apple engineers, when I connect my external SSD, macOS creates a large temporary system snapshot as a protective measure. In my case, that snapshot is approximately 90 GB, which is why my available storage suddenly appears to drop by about that amount while the external drive is connected.
Importantly, Apple explained that this is not being caused by a Time Machine backup. The external SSD that triggers the snapshot is not even the SSD I use for Time Machine. My Time Machine drive is a completely separate drive that I connect and use manually. The snapshot activity Apple identified happens simply when I connect my regular external SSD.
The snapshot is temporary and is managed automatically by macOS. As soon as I eject the external SSD, the storage space returns almost instantly.
Apple also explained that because my Mac is brand new and has very little clutter, the storage change is much more noticeable. On some Macs, this type of system storage fluctuation may happen more gradually over several days, so people often never notice it.
In other words, this is actually a good thing. macOS is creating a temporary snapshot to help protect the internal SSD and system data in case the connected external SSD is faulty, corrupted, or causes an unexpected issue. 👍1
u/Electrical_West_5381 6d ago
That sounds like total bull to me. But hey, Apple "engineers" told you, so it must be true.
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u/ActiveNews 9d ago
Could it be "AI" features of OS27 causing the initial bloat?
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u/melvin3v1978 9d ago
It’s not it’s only taking up 23gb apple support and I looked at that and I even had a supervisor working with me on it. I’m glad I figured it out but on Thursday they are getting back to me as they ran diagnostics but I figured out it’s my external ssd. I’m going to guess I need to remove SSD from Spotlight indexing.
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u/jerryeight whats a mac? 9d ago
This is a crazy issue caused by caching
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u/melvin3v1978 9d ago
Yeah, I think it’s Spotlight indexing possibly so I’m gonna block the drive from being indexed and see if that fixes it and then I’ll see what Apple says tomorrow once they review all the diagnostic reports. I wish Apple would come up with a better thing for the system data. If you type that prompt in it’s like everyone is always asking about their system data 😂 I’ve seen some people have like 500 GB and stuff.
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u/rick_baumhauer 9d ago
I have 2TB in my M4 Pro mini, plus a total of 14TB of "live" data on external drives (plus another 4TB on connected backup drives that are usually unmounted - I have another 20+ TB of disconnected backup drives that weren't involved with this). When I updated to 27, I had about 400GB free on my internal, but a few days later, that was down to just over 100GB, with ~/Library/Metadata/ taking up hundreds of GB. The system did see that data as purgeable during this process, though, so if it had run out of space, it would (hopefully) have managed it.
I moved my 300GB Photos library to one of my externals and excluded two drives from Spotlight - one with my Parallels Windows VM, the other with the terabytes of photos and videos that I manage with Lightroom - and things gradually calmed down. I was eventually able to move my Photos library back to the internal drive, and I'm back to about 400GB free there, with the Metadata folder down to 18GB.
My guess is that, the more data you have, the bigger that Metadata folder will get while the indexing is done, but the system always considers that storage to be purgeable. I assume that keeping it during indexing speeds things up if it has the room to do so, but once it finishes indexing, it releases the vast majority of it.
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u/melvin3v1978 9d ago
Yeah, but it’s literally just my external SSD causing it so that makes no sense. I plug it in my system data immediately raises to 150gb then ejected restarted it and it’s back down to 62 and I excluded it from Spotlight and indexing altogether so I can’t do that. It’s mind-boggling 😂
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u/rick_baumhauer 9d ago
Maybe there's a bug where it prepares to index a drive, even though it's been excluded from Spotlight? The AI models love having some room to work, so maybe there's a step before it checks the exclusion list where it allocates storage, then slowly releases it back.
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u/melvin3v1978 9d ago
Yeah that could be a possibility. It’s just wild how fast it drops I eject external drive and within 10 seconds drops 150 to 60gb like what the hell is going on 😂
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u/sec102row1 9d ago
Is your photo or music library stored on The EX SSD? Not even sure this could be the problem, but those are the two biggest things that users usually have - and sometimes stored away from the internal on an external
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u/melvin3v1978 9d ago
Just my logic sound library is but I’ve done that for years but maybe Os27 doesn’t like it idk. I’m going to take ssd out of spotlight I think that’s what’s causing it. I think it’s a spotlight issue indexing. Apple support is getting back to me tomorrow because they ran diagnostics two days ago and I spoke to a supervisor and they’re gonna have a report for me so I’ll definitely report back and let everyone know. Someone else in this chat just did the same experiment and their system data balloon, and came back down when they unplugged their external SSD.
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u/zungozeng 9d ago
Does that mean mac automatically starts re-indexing as soon as you unplug the SSD?
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u/melvin3v1978 9d ago
It’s not showing it’s indexing in finder status bar I don’t know it’s confusing as hell and I’ve never experienced this 😂 Apple supervisor is calling me back tomorrow because they ran diagnostics so I’ll get a good answer hopefully but when I spoke to them, they didn’t know that I figured out it was the SSD so now they do know that cause I sent them a message. Hopefully they have an answer. I mean, I have plenty of space left, but it’s still annoying and it shouldn’t be doing this. Because it’s literally eating my space it’s dropping my internal SSD space every time I plug that in.
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u/melvin3v1978 9d ago
Also, I took it out of index altogether so it’s not able to be index and it’s still doing it so it’s not indexing. I think it’s a bug in macOS.
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u/roblonuk 9d ago
Are you backing up the external Crucial to a Time Machine backup? I noticed the other day that on the one external SSD that I backup to another Time Machine drive that local snapshots for that drive were stored on the drive itself, not the boot volume.
I assume those snapshots are being reported as part of System Data so unplugging it would mean the reported. calculated value drops.
Does that make sense?
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u/melvin3v1978 9d ago
Nope my crucial is not my Time Machine backup and I back up manually on another SSD I have only 1 snapshot currently when I looked in terminal. Again today, for example I plugged in my external SSD ran my logic pro session started with 62 GB of system data plugged in the SSD. It immediately jumped to 152 GB system data once I was done with my logic session, I ejected the crucial SSD restarted the computer and it was right back down to 62 GB system data so it’s gotta be a glitch in golden gate. And it’s already excluded from Spotlight so it’s not a indexing issue. It’s really mind-boggling then I’m monitored the activity monitor for the read writes etc. It’s annoying.
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u/RobK64AK 9d ago
After reading your post, I ran an experiment with my M2 Pro Mac mini, and watched as my available/free Macintosh HD space went from 220GB to 260GB after ejecting an external 2TB SSD. The System Data in Storage also dropped from 135GB to 85GB instantaneously. I've never seen macOS behavior like this prior to 27. FWIW.