[tahoe-dev] Automatic rebalancing

[James A. Donald]

On 2010-12-06 4:43 AM, Ravi Pinjala wrote:
> I'm pretty sure Ceph runs CRUSH on the servers, too - it's how they
> handle rebalancing, after all. The biggest issue I see there is that
> the way they use it depends on setting a new CRUSH map across the
> entire cluster atomically, which only works on Ceph because they use a
> Paxos cluster to coordinate.

A centralized coordinator is single point of failure and an additional 
configuration issue.  If everyone runs the same algorithm, they will 
mostly agree without need for a central coordinator - though there will 
never be 100% agreement.  If the system tolerates partial agreement 
without hard failure, one can usually do away with central coordinators.