There are some similarities with most blockchain storage solutions and SAFE, mainly that they’re based on something inspired by Kademlia DHT (distributed hash table). Blockchain based solution uses the blockchain for consensus, the DHT is then used to store the data, and there are economic incentives that’s supposed to keep the nodes from deleting the files. SAFE on the other hand has basically extended Kademlia into a solution that can do consensus on it’s own, without the need for a blockchain, by using sections, node aging, data chains etc.
In theory you can also store data directly in a blockchain, but if you want to store a large file on the Ethereum blockchain, the cost might be millions of dollars, compared to a couple cents on SAFE (or on Ethereum Swarm), since every miner would need to process and store it. That’s why they just store the hash of the files instead of the files themselves.
SAFE, Ethereum/Swarm and FileCoin/IPFS all want to some extent to enable a decentralized web. Here there’s also some similarities in how they work, for example Swarm has a chunker that divides a file into small chunks of max 4 kb, a bit similar to what happens on SAFE, except it’s not encrypted and thus doesn’t do the self-encryption process, and a merke tree of the hashes is used to find and assemble the chunks rather than the datamap on SAFE.
The blockchain based solutions only store immutable data in the DHT. This is because the hash of the file is stored in the blockchain and is needed to verify that the file hasn’t been changed in any way. In Swarm there is an implementation of something a bit like mutable data, but it’s based on the Ethereum Naming System (ENS). Basically you have a name like myfile.eth, this points to the hash of your file, whenever you want to change the file, you upload the changes and point myfile.eth to the new hash. This brings scalability issues as need to store a new hash on the blockchain for every single mutation, at the moment that would mean a global limit of less than 10 mutations per second, though sharding will increase this limit once it’s implemented, Raiden too, but not without issues in terms of centralization etc.
There are several big advantages to SAFE compared to the blockchain based solutions. One is as mentioned in another post about securing the data, perhaps there’s some reasonable ways to eventually get this fixed, but even then it runs into the scalability issues of blockchains.
Much of the power and new possibilities on SAFE, compared to the blockchain based solutions, comes from mutable data. Mutable data on SAFE is stored more or less the same way as immutable data, since you don’t need a hash of the data to store in a blockchain. Without a blockchain bottleneck making updates slow and expensive, there are tons more applications that then become possible and clever ways of using mutable data can be used where smart contracts would instead be used on ethereum.
SIACoin is the main solution which doesn’t use a variety of Kademlia. It’s a bit simpler than the others and doesn’t try to do anything more than being a decentralized cloud storage provider, competing against Amazon S3 etc, mainly on price. When you store a file with SIA, a smart contract will regularly check if the node that’s supposed to store still has the file and if it does, pay a reward, if it doesn’t I suppose it takes some copy from another node to make one more to ensure the file doesn’t disappear.
Now, it might be possible that all the issues with blockchains can be fixed, possibly with some new blockchain mutant that’s not really a blockchain any more, but from what I’ve seen on the roadmaps of the various projects for the next few years at least, MaidSafe have come up with something that seems to me to be much more scalable and secure.