[openstack-dev] [Swift] Design note of geo-distributed Swift cluster

Caitlin Bestler Caitlin.Bestler at nexenta.com
Fri Jan 25 18:12:57 UTC 2013

These blueprints and documents are focused almost entirely on how the Swift Proxy creates objects.

I think the more critical issue for Swift objects is how Objects are replicated in a multi-region environment
when a copy becomes unavailable.

The cold hard fact here is that inter-region replication is considerably more expensive than intra-region
replication. If you're doing a multi-region cloud obviously you have to do both, but I am skeptical that
a single algorithm can support both with nothing more than a "distance" metric.

Some serious questions to apply to any design proposal:

* Is each region supposed to be self-sufficient, in that get requests can be fulfilled by a copy within that
    region even if the links to other regions are temporarily down?
* What is the tolerance for "eventual consistency" when dealing with continental distinces and TBs of new
    content potentially being created each day?
* What happens if the same object is updated concurrently in two different regions?

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