[Openstack] SWIFT - Write Quorum

John Dickinson me at not.mn
Tue Sep 9 15:02:49 UTC 2014


I'm not sure what the question is.

If you are looking to have a successful response after it's written twice in a cluster with 4 replicas, no. Swift's quorum calculation is (replicas DIV 2 + 1). This means that for 4 replicas, you have a quorum size of 3. What I would suggest you look in to is the write_affinity setting so that you can do a full-quorum (at least) write to the local region and then asynchronously replicate to the other region. See http://docs.openstack.org/developer/swift/admin_guide.html#geographically-distributed-clusters and https://swiftstack.com/blog/2012/09/16/globally-distributed-openstack-swift-cluster/.

If you are looking to ensure that there is at least one replica in each region, then yes. The quorum size of three (see above) will ensure that, without any write_affinity settings, you'll have at least one replica in each region and two in another before the client gets a 2xx success response code to the PUT request.

--John



On Sep 9, 2014, at 6:59 AM, Brent Troge <brenttroge2016 at gmail.com> wrote:

> 
> 
> If I configure Swift to use 4 replicas across two regions(two replicas per region), is it possible to only list a newly ingested object if it has written at least twice? The goal is to only list a new object only if it has a presence in each region.
> 
> west coast
> region 1 - zone 1
> region 1 - zone 2
> 
> east coast
> region 2  - zone 1( 3?)
> region 2 -  zone 2( 4?) 
> 
> Thanks!
> 
> 
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