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I am trying to understand the concept of storage virtualization. Based on what I have read, storage virtualization appears to be synonymous with cloud storage.

Based on my understanding, Amazon S3 is an example of cloud storage. It is a technology where data is stored on remote cloud servers via API.

How does virtualization factor in cloud storage/Amazon S3, exactly? I mean, what exactly is virtual about Amazon S3/cloud storage? For comparison, In Amazon EC2, we have virtual machines; VMs are virtual computers utilizing the hardware.

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"Real" storage: you identify a disk (or SSD) somewhere. Reads and writes go to that disk.

"Virtual" storage: you issue reads and writes against some identified "virtual disk", but an intermediate layer maps that to some combination of physical disks. There may be multiple disks, multiple written copies, virtual blocks may not be contiguous on physical storage or even on the same device, and so on.

(Yes, RAID is a kind of storage virtualization).

"Blob" storage: you no longer even pretend to have the abstraction called a "virtual disk", and instead write files through an API. Amazon stores them .. somehow. Exactly how is not your concern.

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The word "virtual" means many things in computing, since we rely so heavily in the user interface on representations of what is "real", and re-representations are often just as easy to achieve.

With storage, what is typically considered real is the direct physical attachment of machinery associated with storage, such as a hard risk, and the representation of this facility in the most direct way through the computer's user interface.

When storage is "virtual", it typically deviates from the "real" by being neither physically connected to the local machine, nor connected any separately identifiable remote machine. Instead, it may be represented by the operating system as a local disk, yet physically located elsewhere.

Often words like "virtual" only have meaning in context and in comparison to some conventional or typical arrangement which today's professionals tacitly understand, rather than having a free-standing definition or one that is consistent over time.

For example, a PC with local storage may run a VM, and what appears to be a local storage disk inside the VM in fact passes through a virtualisation layer, and is "really" a file on the disk of the host machine. But whether the storage in such a case is considered "virtual" or not is probably sensitive to context, since the storage itself is still local to the machine, even if the representation inside the guest OS is a virtualised one.

Also, if cloud storage was explicitly represented as such to the user, rather than being falsely represented as a local disk, then it would probably cease to be "virtual" and would become simply another kind of real storage.

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