DistOS 2014W Lecture 14

OceanStore

What is the dream?

• High availability, universally accessible.
• Utility managed by multiple parties.
• Highly redundant, fault tolerant
• Basic assumption was that servers would NOT be trusted.

• Highly persistent
  • Everything archived
  • Everything saved, nothing deleted. "Commits"

• Service was untrusted
  • Held opaque/encrypted data.
• Would have been used for more than files. (eg. DB's, etc.)

• Global ubiquitous persistent data storage
• Nomadic data: It means that data can be cached anywhere unlike the NFS and AFS, where specific servers only can cache the data.
• Untrusted infrastructure
• Cannot delete data, universal archive
  • The easier you delete stuff, the easier you lose stuff

Why did the dream die?

• Biggest reason it died was it's assumption of mistrusting the actors.
  • Everything else they did was right.
• Other successful distributed systems are built on a more trusted model.
• Complexity of the Ocean Store is too great.
  • The solution is expensive.

Technology

• The trust model is the most attractive feature which ultimately killed it.
  • The untrusted assumption was a huge burden on the system. Forced technical limitations made them uncompetitive.
  • It is just easier to trust a given system. More convenient.
  • Every system is compromisable despite this mistrust
• Pub key system reduces usability
  • If you loose your key, you're S.O.L.
  • If you wanted to remove someone' access over an object, you would have to re-encrypt the object with a new key and provide the key to user who wtill have access to object
• security
  • there is no security mechanism in servers side.
  • can not now who access the data
• economic side
  • The economic model is unconvincing as defined. The authors suggest that a collection of companies will host OceanStore servers, and consumers will buy capacity (not unlike web-hosting of today).

Use Cases

• Subset of the features already exist
  • Blackberry and Google offer similar services.
  • These current services owned by one company, not many providers.
  • Can not sell back your services as a user.
    • ex. Can not sell your extra storage back to the utility.

Pond: What insights?

• They actually built it.
• Can't assume the use of any infrastructure, so they rebuild everything!
  • Built over the internet.
  • Tapestry (routing).
  • GUID for object indentification. Object naming scheme.

Benchmarks

• Really good read speed, really bad write speed.

Storage overhead

• How much are they increasing the storage needed to implement their storage model.
• Factor of 4.8x the space needed (you'll have 1/5th the storage)
• Expensive, but good value (data is backed up, replicated, etc..)
• Considerations of importance before making an update
  • burn more storage space as more updates are made

Update performance

• No data is mutated. It is diffed and archived.
• Creating a new version of an object and distributing that object.

Benchmarks in a nutshell

• Everything is expensive!
• High latency

Other stuff

• Byzantine fault tolerance
  • Assuming certain actors are malicious
• Bitcoin
  • Trusted vs Untrusted.
  • It is considered to be untrusted but it takes huge amount of trust when exchanges are made.

What's worth salvaging from the dream?

• Using spare resources in other locations.
• Similar routing system are used in large peer to peer systems.

How to read a research paper

• Start with Intro
  • Figure out what the problem is
• then see the related work for context
• then go to conclusion. Focus on results.
• then fill in the gaps by reading specific parts of the body