Cloud storage is proven to be a lucrative business, estimated at $178 billion as of late 2017. It is believed that Siacoin (SC) will provide a fertile platform for decentralized cloud storage in trustless environments. Sia is a decentralized cloud storage platform that intends to compete with existing storage solutions at both the peer to peer and enterprise level.
Instead of renting storage from a centralized provider, peers on Sia, rent storage from each other. Sia itself stores only the storage contracts formed between parties, denying the terms of their arrangement.
A blockchain, similar to Bitcoin, is used for this purpose. By forming a contract, a storage provider (also known as a host) agrees to store a client’s data and to periodically submit proof of their continued storage until the contract expires.
The host is compensated for every proof they submit and penalized for missing a proof. Since these proofs are publicly verifiable (and are publicly available in the blockchain), network consensus can be used to automatically enforce storage contracts.
Importantly, this means that clients do not need to personally verify storage proofs; they can simply upload their file and let the network do the rest.
In particular, the use of erasure codes can enable high availability without excessive redundancy. Sia will initially be implemented as a blockchain based altcoin, Future support for a two-way peg with Bitcoin is planned
Siacoin (SC) Storage Proof
Through Siacoin (SC), storage proof does not need to have any inputs or outputs; only a contract ID and the proof data are required, Storage proof transactions are periodically submitted in order to fulfil contracts. Each storage proof targets a specific file contract.
Siacoin (SC) Host Protections
A contract on Sia has to be of mutual consent between the storage providers (host) and the clients, allowing the host to reject unfavourable terms or unwanted (e.g. illegal) files.
In other cases, the host may also refuse to sign a contract until the entire file has been uploaded to them. Contract terms gives storage providers some flexibility.
They can advertise themselves as minimally reliable, offering a low price and agreeing to minimal penalties for losing files; or they can advertise themselves as highly reliable, offering a higher price and agreeing to harsher penalties for losing files. An efficient market will optimize storage strategies.
Siacoin (SC) Storage Ecosystem
Sia simply relies on an ecosystem that facilitates decentralized storage, the use of arbitrary data field can be adopted by the storage providers to announce themselves to the network. This can be done using the standardized template that clients will be able to read.
Clients can use these announcements to create a database of potential hosts and form contracts with only those they trust. Hosts are vulnerable to a denial of service attacks.
Clients can use erasure codes, such as regenerating codes to safeguard against hosts going offline. These codes typically operate by splitting a file into n pieces, such that the file can be recovered from any subset of m unique pieces. (The values of n and m vary based on the specific erasure code and redundancy factor.)
Each piece is then encrypted and stored across many hosts. This allows a client to attain high file availability even if the average network reliability is low.
As an extreme example, if only 10 out of 100 pieces are needed to recover the file, then the client is actually relying on the 10 most reliable hosts, rather than the average reliability.
Availability can be further improved by re-hosting file pieces whose hosts have gone offline. Other metrics benefit from this strategy as well; the client can reduce latency by downloading from the closest 10 hosts or increase download speed by downloading from the ten fastest hosts. These downloads can be run in parallel to maximize available bandwidth.
The fundamental idea behind Siacoin (SC) is that as opposed to leasing storage capacity from a national bank of networks (as is the trend with conventional cloud-backed platforms), users of the Sia platform hire storage from each other by means of its distributed storage platform that runs on the cloud. Sia enables the formation of storage contracts between peers.
Contracts are agreements between a storage provider and their client, defining what data will be stored and at what price. They require the storage provider to prove, at regular intervals, that they are still storing their client’s data.
Contracts are stored in a blockchain, making them publicly auditable. In this respect, Sia can be viewed as a Bitcoin derivative that includes support for such contracts.