Time Machine may exhibit an issue in which backups get stuck indefinitely, persistently displaying the message “Waiting for index to be ready.” This problem can occur via both drives connected physically (USB or FireWire) and wireless Time Capsules.
Delete Spotlight index. The most commonly successful fix for this issue involves deleting the Spotlight index from the destination (backup) drive then reestablishing the Time Machine process. Follow this procedure:
- Disable Time Machine in System Preferences
- Download Hidden Files to view invisible files on your mounted drives.
- Delete the file .Spotlight-V100 from your startup drive and the destination disk (the one to which your Time Machine files are backed up)
- Allow the Spotlight index to rebuild
- Turn Time Machine back on
Do not put hard drives to sleep. Open System Preferences and choose “Energy Saver.” Deselect the option to “Put the hard disk to sleep when possible” then reattempt the backup.