Mac Forum / Applications / Mac Applications / May 2008

I absolutely concur

This is a relatively slow way (but I admit I used it myself).

Alternately, in case you are doing a network backup (e. g. over wifi),
you can lock the created disk image (the one with .sparseimage at the
end) to a maximum size smaller than the complete disk.

This way you sort of get the best of two worlds: a TM backup that does
not choke your disk without partitioning nor deleting yourself lots of
old things by hand.

I say "sort of", because indeed there is a remaining complexity, which
is the terrrrible terrrrminal command you have to issue to indeed
constrain the .sparseimage size. But this you only have to do once ;-)

If you are courageous enough (don't come back here tell me I mangled all
your backed up data!) an example Terminal command to redefine the max
size to (here) 50 Go looks like:

Macintosh:~ herve$ hdiutil resize -size 50g -shrinkonly
/Volumes/USBStorage-1/iMac\ from\ Hervé_000a9598f3c2.sparsebundle

In more general terms:

[your prompt] hdiutil resize -size [your size in Go]g -shrinkonly
[drag'n drop here the .sparseimage icon, Terminal will type the path]

After this, depending on the actual current size of your image, you
wait. From very little up to 10 or 20 mn, yes, on a slow wifi with an
already-80-Go image. Wait and don't panic -leave the macbook plugged ;-)

In the end (when Terminal gives you back the prompt) run TM prefs, see:
the new max size is there.

Ah. Of course, before all of this, please take care to turn TM *off*!

I have used this trick to maintain three TM backups (from three
machines) on the same NAS remote disk without perturbations for 5 months
now. Some have reached the allocated max, in which case TM automatically
starts removing oldest things first. None bothered the neighbors, and I
still get the extra space I wanted.

Hervé