iOS: Apple logo with progress bar after updating or restoring from backup
After updating iOS, restoring from a backup, or erasing your iPhone, iPad, or iPod touch, the device displays the Apple logo with a progress bar.
When this occurs, the progress bar may appear not to move, or to be moving very slowly.
Let the device complete the update, restore, or erase process.
The progress bar indicates installation progress. While this process can take as little as a minute if the device has little or no customer data or if the device is being erased, when the device contains a large number of files, the process can take from several minutes to an hour to complete. The amount of time depends on the number of files on the device and whether you're erasing, updating, or upgrading your iOS.
If your device appears in iTunes and allows you to configure sync options and sync content, the process is complete. Leave your device connected to iTunes and wait for the migration process to finish.
If you're updating over the air, keep your device connected to a power source to ensure that it doesn't run out of power during this process. If your device does run out of power, connect it to a power source and turn on the device to let the update or restore complete.
In some cases, you may see the progress bar complete and then start again.