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Purgeable space in macOS High Sierra

T

tomviolence

macrumors member
Original poster
Jan 16, 2012
58
15
I realise there is a lot of options when it comes to macOS’s indication of ‘purgeable space’, but here goes…

Fact #1: I do not save anything with iCloud, but a few measly megabytes worth of Reminders, Notes, Calendars and Keychain. Apart from this, everything iCloud is turned off.
Fact #2: ‘Optimise storage’ in System Information is turned off.
Fact #3: Time Machine ‘automatic backups’ is turned off, and I have recently made a TM backup.
Fact #4: I have about 15GB worth of local, archived Mail storage (under ‘on my Mac’), 1GB of IMAP/Exchange Mail storage, and about 2GB of iOS backups. (About 18GB in total.)
Fact #5: Now, I have about 18GB of ‘purgeable space’ when I look at my HD in ‘Get Info’.

Question #1: Am I to understand/fear that macOS High Sierra might delete my local, archived Mail storage when it needs the space?

Question #2: If not, what else could the ‘purgeable space’ indicate?

I didn't have this problem with macOS Sierra, where – with all the above settings – I would hardly get any ‘purgeable space’ indication, except the GBs worth of iOS backups and the IMAP/Exchange Mail storage.

Much obliged.
 
No, it won't delete your local mails. High Sierra makes a snapshot before each OS update, probably it's this the cause of your "purgeable space".
 
from what I gather purgeable space is temp files that will get auto deleted when required.

so I have been told. the person who told me this could be wrong.
But they work for a 3rd party Mac repair shop so I hope he knows his stuff.
 
elf69 said:
from what I gather purgeable space is temp files that will get auto deleted when required.

so I have been told. the person who told me this could be wrong.
But they work for a 3rd party Mac repair shop so I hope he knows his stuff.
Click to expand...


Purgeable space includes temp files, local TM backups, data also stored in iCloud that you don't strictly speaking need locally (as long as you have an internet connection), and perhaps more
 
tomviolence said:
Thanks for your reply. What purpose does this ‘snapshot before each OS update’ serve?
Click to expand...


Snapshots on APFS disks means that you can basically rollback the entire machine to exactly how it used to be when the snapshot was taken, without it taking up very much space (because of copy-on-write).
To delete the snapshot, use the tmutil command in Terminal (read the man page for the exact argument needed).
 
casperes1996 said:
Snapshots on APFS disks means that you can basically rollback the entire machine to exactly how it used to be when the snapshot was taken, without it taking up very much space (because of copy-on-write).
To delete the snapshot, use the tmutil command in Terminal (read the man page for the exact argument needed).
Click to expand...
Thanks for the clarification.

Question: Would turning off Time Machine entirely (and reverting to other backup software like CCC) stop the OS from making these local snapshots? Or is it inherent to the way APFS works, no matter what backup system you use?
 
tomviolence said:
Question: Would turning off Time Machine entirely (and reverting to other backup software like CCC) stop the OS from making these local snapshots? Or is it inherent to the way APFS works, no matter what backup system you use?
Click to expand...

It's not TM exactly. It's High Sierra on APFS drives specifically. Even someone who's never used TM will have this behaviour. It uses the Time Machine CLI to interface with though, which makes good sense too, since it's also the Time Machine interface you use to revert to the snapshot (from recovery mode).

You can also create your own snapshots at will, so if someone else wants to borrow your computer for a week, and you want them to be able to install and do what they want without you having to deal with it when you get it back, you can also create new snapshots with tmutil (again refer to man-pages. Think it's just tmutil snapshot though). Then you revert it when you get the computer back and everything that was done since the snapshot was made will be gone.
 
casperes1996 said:
It's not TM exactly. It's High Sierra on APFS drives specifically. Even someone who's never used TM will have this behaviour. It uses the Time Machine CLI to interface with though, which makes good sense too, since it's also the Time Machine interface you use to revert to the snapshot (from recovery mode).
Click to expand...
Thanks again for clarifying.
 
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