I have an original 24" aluminum 2.4GHz and it has been acting very strangely lately, and would not boot yesterday. Luckily I had a clone and booted from that, and on bootup I got the message that the internal disk could not be repaired and to backup and format the disk as soon as possible. However, trying to partition the disk gave "could not unmount"; does "erase disk" do a format?. All of the data appears to be on the disk and accessible, but read only, so it makes me wonder if the hard disk is really bad or if this is some other error. I am going today to buy another external disk so that I can have a clone of my clone (now boot) disk just in case. If the internal disk is bad then it is probably easier just to use an external and forget about the internal; I looked at the teardowns on ifixit and it looks like a very time consuming (but not necessarily difficult) process to replace the disk.