Somehow - My Time Capsule Has Insufficient Memory For A Back Up

Question

I have a 1 TB Time Capsule.
I recently got an email from apple stating that my mac is affected in a batch that has hard drive issues and was advised before taking it in to back up my mac. Before the email came through out of the blue, my Mac had lost about 300-450 GB of space overnight on something which was fairly worrying. So when I went to back up today, I got a message stating that my time capsule didn't have enough memory to back up my mac which is odd because I always thought that it deleletd the oldest back ups to make room for the new ones. Anyway after now wiping the time capsule clean so it has 1TB free again (which matches my Macs memory of 1TB) I thought I would give the back up another try and to my surprise no such luck. I got this message:
"This backup is too large for the backup disk. The backup requires 1.01 TB but only 997.05 GB are available.
Time Machine needs work space on the backup disk, in addition to the space required to store backups. Open Time Machine preferences to select a larger backup disk or make the backup smaller by excluding files."
Now, by checking my Macintosh HD disk, it states that I have approximately 150GB free at this present moment in time. Another thing about that message that conceres me is that it says 1.01TB which is impossible because I only have a 1TB machine!!
It's all rather worrying and the best thing is I can't sort my hardrive out until I back it up which is proving to be quite the task. If anyone could shine some light on the siuation I will be very greatful.
Thanks
Matt

Answer 1

So based on what i understand, you have less than, 900 gigs of data and time machine is telling you otherwise. Obvious question to ask you is whether or not you emptied out your trashcan.
If you did empty it out and there is STILL some kind of "phantom like prescence" claiming your hard disk i would look to hidden files as holding the key to your answer.
There is a hidden folder on the top level of your boot disk named ".volumes" which sometimes may contain data that you sent to the trash, without actually deleting it.
In my experience this is caused by sending items to the trash on (typically) EXTERNAL mounted volumes that  have not yet been "deleted" or emptied. i encourage you do a little more reserach before you go ahaed and "show all files" and start deleting random crap, and i would STRONGLY encourage that in the MEAN TIME, forgo time machine and do a finder copy of the things that you cannot live without.
Or do a time machine backup to a 1.5 or 2tb something. I know this is all a little overwhelming, but with the potential failure of the internal drive on your mac, the BEST option for you right now is to backup to a larger volume. If you cant afford a new drive right now, perhaps maybe you can buy it now and return it within a 14 day return policy or something like that. THe important thing is, if your hard drive in your iMac fails, your looking at a VERY costly procedure to recover data from a 1000gb volume.
Better safe than sorry.