Why can't Ubuntu see any free space?

I've got an external terabyte drive to store my scrap (actually I mean a partition on it, I've got some other partitions there). The FS used is ext3. Even after I delete some files there (so there are at least some hundreds mibs free), Nautilus shows zero free space there and does not allow to even create a directory. How to fix this?

I use Ubuntu 10.10 daily build, last updated ton the day before yesterday (Oct 03, 2010).

ext2/3/4 filesystems have a certain percentage of blocks reserved for a "privileged" user; a filesystem might appear as "almost full" yet only root can write to it. My guess is that you are hitting this limit.

By default 5% of the total filesystem size is reserved for the root user. Both the reserved percentage and the "privileged" user can be changed with the tune2fs command.

To change the percentage of reserved blocks to 1%, run (as root):

tune2fs -m 1 /dev/your_disk_partition_device

You can also set the reserved blocks percentage to 0, thus effectively disabling this feature on a certain partition.

To change the privileged user, run (as root):

tune2fs -u username /dev/your_disk_partition_device

More details on both options on the tune2fs man page.