Apple - How do I clear the purgeable area on my disk?

You can create a huge file that will force macOS to clean purgeable files to free you space. Do do so, type this command in a terminal:

dd if=/dev/zero of=~/hugefile bs=15m

It will create a file called hugefile in your home folder, which you can check the size with Get Info and stop when it's big enough for you, using ControlC. Or you can simply let it run until you are out of space in the disk and things start to stop working.

This command takes a long time to allocate the memory, you can also stop it when it's 5~10GB and duplicate the file CommandD to create copies and speed up the process.

Then, you just need to delete the files, obviously.

In your case, you already have the file you want to copy, so you could split it into 50 GB chunks and copy one chunk over. Then let the system purge files and repeat. Once you have all the data over, you can combine them - adding the second file to the first, deleting the second file, etc...

• How to merge files after using split command from terminal?

The main problem is that “purgeable” space is not one monolithic item - it is potentially local time machine or filesystem snapshots, cached data, derived data, iCloud photos at full resolution that will be downsampled as you start to get closer to no free space available.

The system will self correct if you can bring the data over in two pieces in your case, or in n-pieces in the general case.

If time machine is the taking the space, than using tmutil can help. List of snapshots can be checked using:

tmutil listlocalsnapshots /

And cleanup upto 100GiB using:

tmutil thinlocalsnapshots / $((100 * 1024 * 1204 * 1024)) 4

Last two arguments are:

• amount of space to try to reclaim (using $(( )) to calculate 100 GiB)
• urgency, 1 is default, 4 is highest (didn't find better description)

There is a mention of tmutil in a comment, but not of thinlocalsnapshots.

I was able to cause the purgeable area to get cleared by copying over temporary smaller files which eventually caused the purgeable space to be cleared. Once the large purgeable area was cleared then I could delete the temporary smaller files and copy the large one that I intended.

Note, that deleting the smaller temporary files caused my purgeable area to grow again, fortunately it grew small enough that I could copy the large file over. Hopefully Apple refines this over time.