iCloud backup larger than amount of data uploaded. How?

[Morac]

I had an iCloud backup of my iPad Pro which was taking up 4.2 GB of space according to the iCloud storage. That seemed a bit large since the iPad Pro was restored from a backup of a different iPad that was 3.5 GB, but whatever.

Today I ended up doing a backup, restore and restore from backup with iTunes on a Windows PC. Since I wanted to start a fresh iCloud backup, I deleted the existing one. About an hour later I kicked off a backup on the iPad. It finished in about 15 minutes and claimed the backup was 3.7 GB (despite originally estimating 4.2 GB). My Internet upload speeds are 10 Mbps, so there’s no possible way 3.7 GB could have been uploaded in 15 minutes. It would take at least 50 minutes to upload 3.7 GB. At most the backup could have uploaded 1 GB.

I’ve seen this in the past, where backups occur much too quickly to be the size icloud says they are. That leads me to ask, how is the backup larger than the data uploaded? I can only think of two possible explanations:

1. The backup data isn’t actually deleted when you delete it and iCloud just reused the existing backup data. This goes against what Apple claims.

2. iCloud can use data from the backup of one device in another. The backup of my iPad Air 2 likely has some of the same data as my new iPad Pro since that backup was restored. That doesn’t seem right either though.

3. The reported size is wrong and improperly “stealing” storage.


Does anyone know how iCloud backups work enough to explain this?

 

[zorinlynx]

Sort of a combination of (1) and (2) in your post.

iCloud doesn't immediately delete data when you actually delete and it can take up to 30-40 days for the data to actually be removed from Apple's servers. Your iCloud usage quota doesn't count this deleted-but-still stored data.

They do this so that if you accidentally delete something, you can get it back when you call support.

iCloud also uses de-duplication to prevent the same data from being uploaded and stored more than once. Since this data was already in iCloud (in the "to-be-deleted" queue), the de-duplication came into play and it didn't have to upload all of it again.

 

[NickYoung]

This topic seems interesting. I think it might because you have already synced files like photos and messages (could contain many photos) via iCloud so that if you enable iCloud Backup, these files would be automatically sorted into your iCloud backup in the server and you feel iCloud using your old backup.
You could check the estimated iCloud backup size before backing up your iPad Pro by going to iCloud > Manage Storage > Backups > [your device]. You could see that App data could take much storage, switch off the button and iCloud would not backup data in that app this time.

 

[Morac]

So I deleted my iCloud backup because 2 apps were backing up a total of 2 GB despite the data only being 300 MB between the two. I then rebooted and set up backup again and kicked it off. According to my router backup uploaded about 310 MB, which is close since the backup took 10 minutes and my maximum upload speed is 11 Mbps. The backup was 2.4 GB according to iCloud.

So once again somehow iCloud resurrected over 2 GB of deleted data.