Hi Rob,

Do you use Time Machine for backups to an external drive?
TechTool Protection might not be inaccurately reporting a lack of free space on 
the volume.  
If you open Apple System Profiler or Apple System Information, it should agree 
with TechTool Protection. The Finder is not taking into account two types of 
data:

1. Backups that were stored locally because the intended destination volume was 
not available when the backup was created. Time Machine stores these backups, 
called Local Snapshots, in the invisible folder named /Volumes, in an invisible 
folder named .MobileBackups. Please see Time Machine MobileBackups: Apple 
Support Communities.

2. The data used to keep track of versions of files (the feature introduced in 
Lion), which is stored in an invisible folder named .DocumentRevisions-V100 at 
the root (top) level of the volume.

In Apple System Information (About This Mac-->More Information), there is a 
Storage tab at the top of the window. The Storage tab shows disk space 
allocated to backups. The Finder does not take that disk space into account.

Cheers,
Ronni
Sent from Ronni's iPad4


> On 1 Mar 2017, at 5:08 pm, Rob Phillips <r.phill...@iinet.net.au> wrote:
> 
> Since we've been discussing TechTool Pro, can someone advise about this issue 
> I have.
> I have set up TTP to warn me when my free disk space goes down to 15%. See 
> below.
> 
> However, I am getting this message when I have 253GB of 1000Gb free - 25%. 
> This is an SSD drive.
> 
> Are there some cache files which are taking up the other 100Gb? How do I 
> clear these?
> Cheers
> Rob
> 
> -------- Forwarded Message --------
> Subject:      TechTool Pro Failure Alert
> Date: Wed, 01 Mar 2017 16:47:21 +0800
> From: r.phill...@iinet.net.au
> To:   r.phill...@iinet.net.au
> 
> TechTool Pro Failure Alert
> 
> The machine can be located by the following information:
> 
> Date & Time: 1/3/17, 4:47 pm
> 
> User Name: rphillip
> 
> Computer Name: macbook-pro.local
> 
> Computer Address(es): , fe80::a4fb:91ff:fece:89f1%awdl0
> 
> Mac OS X: Version 10.12.3 (Build 16D32)
> 
> Failure/Warning:
> 
>       The volume "Macintosh HD" has 15% free space remaining. The Volume 
> Usage threshold is configured in the TechTool Protection Mac OS X System 
> Preferences pane.
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