I'm running into an issue with sparse bundles. I am using 10.9.5.

The issue is this: deleting files off of a sparse bundle does not actually free 
up space, or at least does not appear to.

Specifically: the partition that I'm using for Time Machine had a sparse bundle 
created in it. The sparse bundle was the size of the partition minus a small 
amount (default sizing). Due to the poor speed of Time Machine with sparse 
bundles and the default band size, I used the technique seen in various places 
to make the band size bigger (copying it with hdiutil and specifying a new band 
size).

"hdiutil compact" will not free up unused bands when they are bigger than the 
default (128 mb in use). I did not think this would be a concern, because even 
if all of the drive image space is allocated, there will still be space on the 
virtual disk that is unused, freed up, and will be reused. The worst that would 
happen, I figured, would be that the band files would be rewritten repeatedly 
with new backup data.

This is not what happened. Issue number one, is that the free disk space that 
the operating system reports is based on the free disk space of the underlying 
physical disk, regardless of how many gigabytes of data have been deleted off 
of the this image. (As you can guess, this means that my entire Time Machine 
history is now gone.).

Issue number two? For some reason, just ignoring the disk free result, 
attempting to write to the image drive anyways fails. Nevermind that the HFS 
filesystem contained on the drive image should have terabytes of unused space, 
writes fail. It started with backupd complaining that it could not write its 
log file, and now I cannot even use a simple "echo test > out" without a 
complaint.

First question: is there any way to make a sparse image drive reuse space in 
the bands when they are freed up?

Second question: is there any way to compact a sparse image when the band size 
used is bigger than normal?

(A monthly maintenance reboot into 10.12, or something similar, is not out of 
the question. For normal operation, I need features of 10.9.5 that go away in 
10.10.)
---
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