The latest iPhone restore bug I've been tracking is a great example of unintended consequences. Now that we have iPhones with really large storage capacity, we also have REALLY large files in iPhone backups and REALLY large backups in general. I've started seeing a few examples where these large backups crash the restore program on the iPhone. This is one (of many) causes for the error message “iTunes could not restore the iPhone because the iPhone disconnected.”
I want to repeat here that there are A LOT of causes for the iPhone disconnected message. So much so, that I've written about this error message before here and here, but I thought the iPhone restore crashing causing the disconnected message was new and fun enough to get its own post. When this is the problem, you'll also see the restore progress bar move (usually for hours) before the disconnected error occurs (although you'll probably be sleeping when it happens, because you'll have left the restore going overnight!). When the progress bar is stuck too, that's usually a different cause.
So what do you do when the backup is too large to restore? Well, first I want to make a plug for Decipher Backup Repair. MOST of the time, if the backup is causing the ”disconnected” error, there is really an issue with the backup that needs to be fixed, and we've designed Decipher Backup Repair to scan and fix the errors for you. If Decipher Backup Repair doesn't help restore the backup, as part of our customer service, we'll help see why the backup isn't working, and see if this restore crashing issue is the problem. If so, we'll likely help you trim down the backup to the essentials, so that it's small enough to restore without crashing the backup process.
Also, I want make sure I mention: If you're getting the “disconnected” error while MAKING a backup, you don't want to do a restore -- that will overwrite and erase your data! Instead, you should check out the section “iPhone Disconnected Error During a Backup” in this other blog post I wrote. That article will talk about steps you can take to fix errors while making a backup in iTunes.