Hi, hope someone can help: I have an early 2008 iMac with a 500GB hard drive (currently 433GB used) I have a Verbatim 500GB external drive which I have just erased (format: MAC OS Extended (Journaled), (says 499.32GB is free) I went into settings, Time Machine, and selected the external drive to use for backups, however Time Machine reports the following error, and I don't understand why 516.38GB is required, when my hard drive is only 500GB. "Time Machine could not complete the backup to external hard drive This backup is too large for the backup disk. The backup requires 516.38 GB but only 499.32 GB are available. Time Machine needs work space on the backup disk, in addition to the space required to store backups. Open Time Machine preferences to select a larger backup disk or make the backup smaller by excluding files."