#NO, they are NOT synonyms.

##The "Online" in Online Storage refers to the AVAILABILITY of the storage, not it's mode of access or location.##

##Cloud Storage is a type of Online Storage:##

Storage Availability generally comes into 3 camps:

• Online Storage:

  Is storage that is already "mounted" and accessible immediately (there may lag or delays inherent in the system, but there are no prior steps required to "prepare" the storage. Examples would be a local hard drive, a plugged in USB drive, a plugged in external hard drive, a CD/DVD in the drive with raw file system files that can be seen and accessed through the file system at the moment (the drive has already been mounted), network storage (file servers, NAS, SAN, and Cloud Storage)

• Nearline Storage:

  Is storage that needs to be first mounted (sometimes by a system administrator) in order to be accessible. Examples include a USB or external drive not plugged, a Virtual Drive that must be loaded or mounted by a Virtual Manager like HyperV, VMWare, or Oracle's VirtualBox, a backup "Image" of partition or drive created by something like Ghost, or Acronis, a .IMG or .ISO file image of a CD/DVD created with burning software that you then MOUNT as online storage (if you use it to BURN a DVD/DVD... then you are RESTORING a BACKUP and in this way, it is Offline Storage)

• Offline Storage:

  Is storage that resides in a backed-up form. That is, it's usually compressed, possibly encrypted, and possibly contains only the DELTA (changes) from the last backup. These techniques are ll part of Storage Management strategies and solutions that make point in time snapshots and rolling backups possible, timely, affordable and therefore feasible.

  However, the data stored CAN NOT accessed in this backed-up form. It must first be RESTORED to either Near-line Storage (then mounted) or Online Storage

##How They Work [Together] In Practice##

None of above terms (Online, Near-line, or Offline) necessitate actual Cloud Storage... which is what an end-user interfaces with, whether with a web page/web GUI, or an API, or a desktop app that allows syncing and access through the PCs file system). Cloud Storage data may be stored in one or more physical locations (e.g. datacenters) with pipes to the Internet

In Enterprise systems which constitute more than 80% of all data in actual storage, these concepts are staples as all Enterprises with large data needs, including Cloud Storage Provider like DropBox, or Box.net, or Google Drive all must manage their Storage for either internal and/or external use (as the Storage as a Service product/service that they provide to their customers).

Therefore, all enterprises use some combination of Online Storage, Offline Storage, and Nearline Storage on their "back-end" to manage, serve, and backup/ensure service continuity.

In addition, a Cloud Storage Provider might have 1, 2, or all 3 forms of storage as part of a Storage Management strategy that allows the provider to do business... in his case, PROVIDE Cloud Storage.

As far as the consumer is concerned... this Cloud Storage is online (because it's "immediately available" as long as it is available through his file system (with the use of a syncing desktop app) or even in an app or web interface, so long as that is the primary interface with which the user gets to all his files e.g. the user primarily uses a web browser/web apps (either on desktop, or they only have a Chromebook, let's say) to do work, such as Google Docs to create documents and stores and retrieves them on Google Drive or DropBox.

But, once again, in order for the Cloud Storage Provider to provide the data Storage As A Service, he may need to employ 1-3 forms of Storage (Online, Nearline, and/or Offline).