So, I have a 2010 MacBook Air which came with a 256gb SSD. On "available" space on Get Info, it lists 250gb available. Now, OK, I know that typically this value is not identical to the sold size of the drive. But my rather elderly MacBook Pro, with a 320gb HD, still lists 319.21gb available. So does that mean that 6gb of my SSD cells have already rotted, in spite of the machine not being used all that much? If so that's... worrying!