Review

To provide large storage facility, decentralized systems aggregate the available disk space of participating computers. The main purpose of such systems is to ensure durable storage despite of nodes failures. Unfortunately, in practice most of the assumptions about independence of failures are not true.

Glacier is a distributed storage system that relies on massive redundancy to mask the effect of large-scale correlated failures. Main goals fo the system: durable, decentralized storage despite Byzantine failures of a majority of participated nodes.

Proposal

The system’s main distinction is absence of any assumption about the nature and correlation of faults. Preventing data loss even under extreme conditions (85%) should be achieved.

Existed systems:

OceanStore and Phoenix. Apply introspection to defend against the treat of correlated failures. They are rely on observing actual failures and looking at the configuration of the system respectively. Main problem of such systems is to build really detailed failure model. TotalRecall uses introspection as well to optimize availability under churn. OceanStore uses separately mechanisms to maintain short-term availability and long-term durability. But it can not sustain Byzantine failures.

Conclusions

The paper more concerned about the failure and security aspects. Author’s presented the design and evaluation of the system. The system uses erasure codes and garbage collection to mitigate the storage cost. They found that the storage overhead can be substantial when the availability requirements are high and a large fraction of nodes failed.

Advantages:

  • High durability
  • Far less vulnerable to large scale failures

Disadvantages:

  • No remote write/update
  • Excessive Redundancy within the storage system, in order to ensure high fault tolerance
  • Lifetimes storage data are limited.

Volunteers:

Due to its high reliability, and security, this storage system is suitable for Volunteer computing. However since there’s no remote write and update, this system could be used purely as an archival storage of computed data.

decentralized_storage_systems/glacier.txt · Last modified: 2012/04/23 00:54 by julia
 
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