docs/_storage/overview.md

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A decentralized storage architecture

The Blockstack Network stores application data using a storage system called Gaia. Transactional metadata is stored on the Blockstack blockchain and user application data is stored in Gaia storage. Storing data off of the blockchain ensures that Blockstack applications can provide users with high performance and high availability for data reads and writes without introducing central trust parties.

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Understand Gaia in the Blockstack architecture

The following diagram depicts the Blockstack architecture and Gaia's place in it:

{% include architecture.md %}

User control or how is Gaia decentralized?

A Gaia hub runs as a service which writes to data storage. The hub service writes to data storage by requiring a valid authentication token from a requestor. Typically, the hub service runs on a compute resource and the storage itself on separate, dedicated storage resource. Typically, both resources belong to the same cloud computing provider.

Gaia's approach to decentralization focuses on user control of data and its storage. If a user can choose which Gaia hub provider to use, then that choice is all the decentralization required to enable user-controlled applications.

The control of user data lies in the way that user data is accessed. When an application fetches a file data.txt for a given user alice.id, the lookup will follow these steps:

1. Fetch the zonefile for alice.id.
2. Read her profile URL from her zonefile.
3. Fetch Alice's profile.
4. Verify that the profile is signed by alice.id's key
5. Read the gaiaHubUrl (e.g. https://gaia.alice.org/) out of the profile
6. Fetch the file from https://gaia.alice.org/data.txt.

Because alice.id has access to her zonefile, she can change where her profile is stored. For example, she may do this if the current profile's service or storage is compromised. To change where her profile is stored, she changes her Gaia hub URL to another Gaia hub URL from another hub provider. If Alice has sufficient compute and storage resources herself, she may run her own Gaia Storage System and bypass a commercial Gaia hub provider all together.

{% include note.html content="Users with existing identities cannot yet migrate their data from one hub to another." %}

Applications writing directly on behalf of Alice do not need to perform a lookup. Instead, the Blockstack authentication flow provides Alice's chosen application root URL to the application. This authentication flow is also within Alice's control because Alice's browser must generate the authentication response.

Understand data storage

A Gaia hub stores the written data exactly as given. It offers minimal guarantees about the data. It does not ensure that data is validly formatted, contains valid signatures, or is encrypted. Rather, the design philosophy is that these concerns are client-side concerns.

Client libraries (such as blockstack.js) are capable of providing these guarantees. Blockstack used a liberal definition of the end-to-end principle to guide this design decision.

Gaia versus other storage systems

Here's how Gaia stacks up against other decentralized storage systems. Features that are common to all storage systems are omitted for brevity.

Features	Gaia	Sia	Storj	IPFS	DAT	SSB
User controls where data is hosted	X
Data can be viewed in a normal Web browser	X			X
Data is read/write	X				X	X
Data can be deleted	X				X	X
Data can be listed	X	X	X		X	X
Deleted data space is reclaimed	X	X	X	X
Data lookups have predictable performance	X		X
Writes permission can be delegated	X
Listing permission can be delegated	X
Supports multiple backends natively	X		X
Data is globally addressable	X	X	X	X	X
Needs a cryptocurrency to work		X	X
Data is content-addressed		X	X	X	X	X