PS3 reports wrong free space on external HDD
here's the story: I decided to upgrade the internal HDD of my PS3 with a larger one (500GB!), so I wanted to make a backup (I have a lot of savegames and many downloaded PSN games).
I connected and external HDD I used before (to make a backup, but also to play movies, music and such), so I'm confident it works correctly. The PS3 reports 21GB free on the disk, but for the backup it needs 6GB more, so I connect to my PC, I delete about 9GB of stuff (now I should have enough space) and connect back to the PS3, which still reports 21GB free! My PC instead reports the correct free space. I try to make a backup anyway, but it says that it still needs 6GB.
Strange, I say, so I decide to use a different external HDD (which, as the previous, I have used before). Same story, he PS3 reports 7GB free, I delete enough stuff, connect back, but it stills reports 7GB, while the PC reports the correct space...
Maybe the PS3 caches information about the disk, but what I'd like to know is: how can I make the PS3 get the correct space? I didn't find any obscure sub-option in the XMB to "refresh" disk information. I tried to disconnect and reconnect the external HDDs, I restarted my PS3, I left it turned off completely for some time, I even tried to change the HDD name on my PC, but nothing changed.
I wouldn't want to make a reset of the PS3's settings (it would just be a nuisance), so any advice would be much appreciated!