Also, just to add to Ronni's post.
If you still find after searching that nothing turns up "large files"
anywhere a couple of other things to look out for are:-
1) backups that are saving back to the original hard drive instead of
another drive (eg Silverkeeper, Time Machine, Deja Vu.) Sometimes if the
"destination drive" disappears it can change the script and save back to
2) invisible system log files. I can't remember off the top of my head
exactly where these ones are, but if you have no joy post back to the list
and I'll check my notes for the location of it.

I've had both the above happen with client where the backup was backing up
to the same drive as the original data was and was eating up the hard drive
And on another occasion had another client who had a corrupt system log
file. As quickly as they were deleting things to make space it was chewing
it back up again. In fact it got down to zero KBs of free space! I was
surprised the machine was still running when I went out there to fix it!
Once I found the hidden corrupt files it returned about 250GB of space back
to them!!

Just a couple of thoughts off the top of my head.

Hope that helps.

Kind regards

On 2/7/11 11:44 PM, "Ronda Brown" <> wrote:

> Hi Pat,
> In System Preferences > Other - TechTool Protection, check the Directory
> Backup Interval.
> If you have it set for every 4 hours, & if it is doing this on every drive
> that is ever connected to your Mac (backup drives / Time Machine etc)  it can
> create a very large folder.
> I had similar to what you have explained below happen on a client¹s computer
> and I checked the TechTool Pro Protection folder and it was over 100GB in
> size!
> The folder containing all the TechTool directory backups is located in the
> main Hard Drive > Library > Application Support > TechTool Protection folder.
> Drag any that are no longer required to the Trash, you will be asked for your
> administrator password.
> Empty the trash when you have finished.
> Restart you Mac.
> Cheers,
> Ronni
> On 02/07/2011, at 10:57 PM, Rob Phillips wrote:
>> Hi Pat
>> I am probably less qualified than others to respond, but in the interests of
>> urgency.... I can think of two causes:
>> your hard disk is rapidly becoming corrupt and there is a decreasing amount
>> of usable space.
>> something is writing huge amounts of stuff to some sort of log file
>> For 1, I'd boot up off the installation DVD (hold down C on startup) and run
>> disk utility. Failing that reboot off the installation DVD in diagnostic mode
>> (hold down D on startup) and run the hardware test.  Techtools might help you
>> here too, but I haven't used these for 5+ years.
>> If 1 is OK, look for files which are very large and increasing in size.
>> Hope this helps, but things might not be looking good...
>> Rob
>> On 2/07/11 10:01 PM, Pat Scott wrote:
>>> Yesterday the boot disk of my Mac Pro suddenly began filling up with
>>> something unknown. Tech tool Pro put up messages saying the disk had only
>>> 13% free space left, out of 320 GB.   The only thing I could think to do was
>>> try to find out where the excess was accumulating.  This seemed to be the
>>> Application Support folder in my Home folder. I moved an assortment of the
>>> folders to another disk (there are 3 disks), and this moved the added GBs
>>> out of the boot disk, so it was back to 140 GB free.
>>> Today I did various jobs on the computer and things seemed normal until I
>>> tried to install Security Update 2011-004. The message came up that this
>>> update could not be installed on the boot disk because it was not suitable.
>>> Then I tried to install the OS 10.6.8 update, and it did install.   I tried
>>> the Security update again, and got the same message. Then Tech Tool Pro
>>> started its warnings again only this time there was only 4% of free space
>>> left and it was going down fast. Within a few minutes it was down to 600MB,
>>> so I shut it down quick.
>>> I am totally at a loss as to what I should do.  To make things even more
>>> difficult, from Monday I have to be away for ten days.
>>> I hope someone can advise me.
>>> Thanks,
>>> Pat
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