Comment 2 for bug 539653

/var/lib/ureadahead/debugfs is just mounted off somewhere on your / filesystem. It has nothing to do with the difference in reported sizes.

The difference is due to a confusion between various tools as to what "GB" means. The installer matches what hard disk manufacturers generally use, so 320 GB = 320 * 1000 * 1000 * 1000 bytes. GParted is apparently reporting in binary units (sometimes spelled "GiB"), and 298.1 GiB = 298.1 * 1024 * 1024 * 1024 bytes, which if you do the sums comes out to about 320.08 GB. So you haven't lost any disk space - you're just seeing different numbers reported by different programs.

Ubuntu has recently adopted a policy stating that: (a) GB must always mean decimal units and GiB must always mean binary units; (b) hard disk sizes are to be reported in decimal units; (c) some other things that aren't relevant here. This policy is controversial for various reasons and we may amend it, but I don't think too many people seriously disagree with the notion that hard disk sizes should be reported in units that match what the label on the disk you bought says, or at least that you should be able to see them in those units.

The installer is abiding by this policy, as in fact it has done since Ubuntu started; but GParted looks as though it ought to be changed to use decimal units rather than binary units.