No space for Win7 backup but hdd 70% empty

I have a second internal 250Gb hdd specifically for Win 7 (64bit) backup and restore purposes which I set up about two months ago. The other day I got an alert/warning that there was insufficient space to complete the current background data file backup. In Control Panel\backup & Restore\ Help I learned the following.

Quote

By default, Windows automatically saves as many system images as it has space for without taking up more than 30 percent of space on the backup disk. Once the disk starts running out of room, Windows deletes older system images. You can set Windows to retain as many system images as it has space for on the backup disk or to only keep the most recent system image. You should always keep the most recent system image. If you are saving your system image on a network location, you can only keep the most recent system image.

Unquote

Applied to my case Win 7 will only use max 70Gb of my hdd whereas at the time of the alert, a third 'period' data file backup would have taken me over the arbitrary 70Gb limit although I still had (and currently have) approx 178Gb of free space on the same hdd. Unless, I have overlooked something, there doesn't seem to be any way of over-riding the 30pct max of available free space imposed by Win 7. I know I could buy a much larger second hdd so that the 30pct would represent more backup space but why should I need to.

Any ideas appreciated.

Thanks
Pedro

maybe I am saying something stupid, but is your drive NTFS formatted?
I had the impression that some formats like FAT32 have a limited "root" for files...

I would truly appreciate if someone could confirm or bust this mith

Pedro38,

If you want more space for storing older images, shadow copy storage area of the target volume would need to be increased. The limit should be able to be changed with either

a) vssadmin Resize Shadowstorage or
b) Control Panel -System -System Protection -configure - Disk space usage.

Pedro38,

thanks for the link, that's exactly what i had in mind, but wasnt sure of the numbers nor how it would apply. I am glad you solved your problem.
cheers