APFS – How to Delete or Show Size of Non-TimeMachine Snapshot

apfshigh sierratime-machine

tmutil not only stores Time Machine snapshots, but also snapshots for other applications. E.g.:

~% tmutil listlocalsnapshots /
com.econtechnologies.chronosync.236A7A4F-5F96-4F99-8559-57D3965BF6BA.1575374525

This is a snapshot from a backup/sync application called ChronoSync.

My question: How can I determine the size it takes on my hard disk, and how can I delete it?

I'm using High Sierra, and there is no hidden /.MobileBackups folder, nor is anything (other than my hard disk) mounted at /Volumes.

Edit: I can mount the snapshot using the following commands:

~ » sudo mdkir /tmp/snapshotbackup
~ » sudo mount_apfs -s com.econtechnologies.chronosync.236A7A4F-5F96-4F99-8559-57D3965BF6BA.1575374525 / /tmp/snapshotbackup

From there, I can determine the size:

~ » sudo du -sh /tmp/snapshotbackup/
204G

Clearly, this is a stray snapshot that is causing my disk to fill. However, that 204G is so large (on a 250 G disk), that is surely contain files also present on my hard disk (I kind of assume APFS uses hard symlinks here). However, I'm hesitant to delete and files from /tmp/snapshotbackup/ fearing I may thus delete (hardlinked) files from my regular disk (not likely, but I prefer to be cautious).

So I still have the question how can I determine the size this snapshot takes on my hard disk, and how can I delete it?

Best Answer

I received a reply from the author of ChronoSync, and he helpfully explained the following option to manage snapshots.

To list snapshots:

diskutil apfs listSnapshots /

To delete snapshots:

diskutil apfs deleteSnapshot / -name <name_of_snapshot>

This seems the better option, which unfortunately doesn't seem listed elsewhere (all other guides I found only mention tmutil). I couldn't test, since I already deleted it with CCC.

1. How big a drive do I need for Time Machine?

A general "rule of thumb" is, to keep a reasonable "depth" of backups, Time Machine needs 2 to 4 times as much space as the data it's backing-up (not necessarily the entire size of your internal HD). Be sure to add the size of the data on any other drives/partitions you want to back up.

But this varies greatly, depending on how you use your Mac. If you frequently add/update lots of large files, then even 5 times may not be enough. If you're a light user, you might be able to get 1.5 times to work, but that's subject to problems any time a large backup is needed.

And, of course, the larger the drive, the more old backups Time Machine can keep for you. A drive that's too small may only have room for a few weeks (or even days) of backups.

Unfortunately, it's rather hard to predict, and most of us have a tendency to add more and more data to our systems over time, so if in doubt, get a bigger one than you think you need now.

Also, there are some OSX features and 3rd-party applications that take up large amounts of backup space, for various reasons. See question 9 for details.

This is a trade-off between space and how long Time Machine can keep its backups, since it will, by design, eventually use all the space available. But it won't just quit backing-up when it runs out: it starts deleting the oldest backups so it can keep making new ones. Thus, the more space it has, the longer it can keep your backups.

If your backup disk is on the small side, and Time Machine needs to do a very large backup, either because you've added or changed a lot or done something like an OSX update since the previous backup, you may get one of the messages in Troubleshooting item #C4 (which one depends on exactly what happened, and which version of OSX you're on.)

My Answer

Then it'll only take a snapshot that's about 120GB in size, and while that same snapshot will grow over time as I take more recent snapshots of my system, it will never go beyond 500GB because that's the maximum size of my internal HDD.

No, not quite. The 1 TB hard drive will be filled up because Time Machine keeps your backups and deletes them once your hard drive is filled. There is more than one backup stored on that hard drive. As stuffe pointed out as well, Time Machine allows you to restore to a previous backup, since Time Machine may keep 7 or 8 backups on that 1 TB hard drive.

I'm asking this because I want to know if I should use a separate external HDD for storing my actual files.

Yes, you should. You should be dedicating a drive to Time Machine. Here is the quoted answer from 3 in the website I linked above:

3. Can I use my Time Machine disk for other stuff?

Yes. Time Machine will not delete anything you put there. But it's not a good idea to put anything else important on the same physical drive, unless you back it up elsewhere. When (not if) that drive fails, you risk losing it.

If you want to do this anyway, it's much, much better to partition an external drive into 2 (or more) parts, also called volumes. Assign one to Time Machine, for its exclusive use for backups; use the other partition(s) however you want. To use a new drive, or one you don't mind erasing, see question #5. To add a partition to an existing drive that already has data on it, see question #6.

MacOS – Clear large .MobileBackups files/folder

All signs point to you not having 400 GB (or even 26 GB of space used from .MobileBackups) and with the repeated edits, I'm not even sure we're on the same page, but for others - here are some things to try:

Rather than re-enabling things, try giving the system 5 minutes to clean up before the restart

sudo tmutil disablelocal 
sudo shutdown -r +5

Then when the machine restarts, look for that folder and delete things using Finder or terminal from /.MobileBackups once the machine is restarted with the local store disabled.

First check for a huge file in / with:

sudo ls -sa1 / | sort -n | tail -4

We know the large files aren't anywhere else but Applications and Users - but you could use this answer to search for smaller files (say 1 GB or larger)

If you're looking to just know what the size of various folders is - this long running command (14 minutes on an SSD MacBook Pro with 200 GB total allocation / 6 minutes on Mac Pro with about the same) will show you a list of the largest folders - hidden or not.

sudo du -smx /* /.* | sort -n

If that folder no longer shows using that space, your next recourse is to see if the filesystem catalog and free space accounting can be fixed. That would be the last step before backing up, erasing and reinstalling the OS.

Boot to single user mode: Hold Command + S when the boot chime is sounded and hold it until white text on a black screen appears.

/sbin/fsck -fy /

repeat the above check+repair until there are no errors and then

halt

Best Answer

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MacOS – How big should the Time Machine backup drive be

1. How big a drive do I need for Time Machine?

My Answer

3. Can I use my Time Machine disk for other stuff?

MacOS – Clear large .MobileBackups files/folder

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