hello its seems a problem has occurred in all my imac Hdd, external harddrive and i have tested on my USB and its has the same problem once in a while. This needs to be solved, since Im at the point when my imac hdd has reached its limit and i need to transfer the memory into an external hdd, knowing its got the same problem. The Problem: Normally when adding a new file into the harddrive the availablity of the memory decreases. easy but i have noticed when im deleting file to gain some extra space, the availbiltiy doesnt increase but it stays the SAME. i tested my USB out, and to fix the problem i always have to reformat it. i had my imac for almost about 9 months now, so i never reformatted my 1tb external hdd or the harddrive in my imac which is 600gb how can i fix this problem? without reformatting and loosing all my data in both hdd's. need help asap!