There is currently no tag storage.
The usage guide for online-storage (with cloud-storage a synonym) is presently:
Storage of files that are available online, also known as cloud storage. Prefer tag [online-backup] where there is an element of automation involved in the transfer of data.
With 3 followers.
The usage guide for image-storage is presently:
Apply to questions about the storage of image files that are available online, also known as cloud storage. Prefer tag [online-storage] where the storage aspect has little or no visual element (such as thumbnails of images) and tag [online-backup] where there is an element of automation involved in the transfer of data and/or retrieval is likely to be infrequent.
With 1 follower.
Usage is relatively low for both (55 and 5 Open Qs for online-storage and image-storage respectively) so whether merged/synonymised or kept distinct would make very little difference in practice now or probably in the medium term, but there is a difference in intended use that though subtle is enough to justify independently retaining both tags (now that they exist).