Time Machine Local Snapshots

Report · Apr 29, 2018

Hi all, I wish to ask if anyone has the same problem, but before please read this few lines that I've copied from DaisyDisk web site:

"there’s a chunk of space that is not literally free, but is nevertheless available to applications. In macOS, it’s called “purgeable space”.

The purgeable space mostly consists of local snapshots of Time Machine, and also caches, sleep images, swap files and other temporary system files.

When an application requests more disk space than is currently free, the system automatically and instantly reclaims the corresponding amount from the purgeable space. Or else, when there is no deficit of free space, macOS allows the purgeable space to pile up to as much as 80% of disk’s capacity, by design.

The system calculates the current amount of purgeable space asynchronously in the background, and often there can be a significant delay between your action and its effect on the purgeable space, from a few seconds to a few minutes."

Now, on an iMac 27" with High Sierra I have a startup disk of 1Tb, with 800Gb of free space. Despite this AE tells me that it does not have enough space to create cache files on that disk. This because - also if in the Finder you "see" 800Gb of free space - in reality, they are not. The true free space is about 40Gb. Deleting the Time Machine local snapshots via Terminal with the "tmutil" command free up space on the hard drive and AE doesn't ask any more space to create cache files.

Just to ask:

- anyone has the same problem? Any solution?

- is AE that do not "communicate" with the MacOs system and tell him to automatically free up space?

Thanks!

- Marco.

Report · Apr 29, 2018

You have to specify in AE Preferences how large the AE Cache will be. It also helps to purge it frequently.

Report · Apr 30, 2018

Thanks for your reply, in fact I have not yet tried to change the size of the cache, I do not know if this helps. In reality it seems that the "real" space left by the operating system is very little, something about 10/20 GB...

Report · Apr 30, 2018

That's an interesting problem to have, and I suspect you don't see too many people with it because Time Machine should really be used on an external hard drive. The way you currently have it set up only offers you protection from accidentally deleting files, and it gives you the ability to go back and retrieve old versions. What it doesn't give you is drive recovery protection—if your hard drive fails then Time Machine on your internal drive will be of no help.

You can also boot into Recovery Mode on a Mac and restore a Time Machine backup to another drive. You might not be able to do this with your setup because that recovery process needs to wipe your drive first. I'm not certain if you can get away with simply having a separate partition that you can wipe.

All this is to say that you should really have an external hard drive for your Time Machine, which would also solve your issue of not having enough space for Ae cache.

Report · Apr 30, 2018

Thanks for your reply, sorry, maybe I did not explain well... Actually I use Time Machine with an external usb drive and it works nice. The problem is that on High Sierra, Apple, implemented this "local snapshots" invisible files located on the startup disk. Usually they must be automatically deleted when space is needed. Unfortunately it seems that AE does not communicate correctly with the operating system, in other words: even if it claims this space the operating system does not delete these local snapshots.

Report · Oct 28, 2018

I have the same issue. I’d like to allow as much space as possible for AE as recommended but time machine snapshots fill up space in High Sierra so I can’t use the space. Upgraded to Mojave but still the same.

Did you manage to clear snapshots using Terminal? It didn’t work for me.

Cheers

steven

Report · Sep 26, 2023

5 years later and the problem consists.
The only work around I found is to delete the snapshots.

Open the Terminal app, and type tmutil listlocalsnapshots /.
Press Return, then wait until you see the list of snapshots.
Type tmutil deletelocalsnapshots xxxxxxx (xxxxxx being name of one of the backups, usually in the form of a date followed by a text string.)
Repeat Steps 1 and 2 to delete other backups.