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It's the "unique-as-possible" placement that swift uses. Since regions are "more unique" than zones, it is placing 3 replicas into 2 regions and needs a couple of rebalances to settle down. What you are seeing is exactly the same as if you had 1 region and only 2 zones.

--John


On Mar 20, 2013, at 9:40 AM, Adrian Smith <adrian_f_smith at dell.com> wrote:

> I'm putting together a simple test cluster across two DCs using the
> new region level. Each DC has two storage nodes, each with two
> devices. The logical setup looks like this,
> 
> region 1
>   zone 1
>      10.21.146.76
>         sdb1
>         sdc1
>   zone 2
>      10.21.146.77
>         sdb1
>         sdc1
> region 2
>   zone 1
>      10.49.123.77
>         sdb1
>         sdc1
>   zone 2
>      10.49.123.78
>         sdb1
>         sdc1
> 
> Obviously this isn't an ideal setup since I only have four zones
> rather than the preferred five but for my basic needs it's fine.
> 
> I create a ring,
> 
> swift-ring-builder account.builder create 10 3 1
> swift-ring-builder account.builder add r1z1-10.21.146.76:6002/sdb1 100
> swift-ring-builder account.builder add r1z1-10.21.146.76:6002/sdc1 100
> swift-ring-builder account.builder add r1z2-10.21.146.77:6002/sdb1 100
> swift-ring-builder account.builder add r1z2-10.21.146.77:6002/sdc1 100
> swift-ring-builder account.builder add r2z1-10.49.123.77:6002/sdb1 100
> swift-ring-builder account.builder add r2z1-10.49.123.77:6002/sdc1 100
> swift-ring-builder account.builder add r2z2-10.49.123.78:6002/sdb1 100
> swift-ring-builder account.builder add r2z2-10.49.123.78:6002/sdc1 100
> 
> and then attempt to rebalance it with,
> 
> swift-ring-builder account.builder rebalance
> 
> The output is...
> 
> Device r1z1-10.21.146.76:6002/sdb1_"" with 100.0 weight got id 0
> Device r1z1-10.21.146.76:6002/sdc1_"" with 100.0 weight got id 1
> Device r1z2-10.21.146.77:6002/sdb1_"" with 100.0 weight got id 2
> Device r1z2-10.21.146.77:6002/sdc1_"" with 100.0 weight got id 3
> Device r2z1-10.49.123.77:6002/sdb1_"" with 100.0 weight got id 4
> Device r2z1-10.49.123.77:6002/sdc1_"" with 100.0 weight got id 5
> Device r2z2-10.49.123.78:6002/sdb1_"" with 100.0 weight got id 6
> Device r2z2-10.49.123.78:6002/sdc1_"" with 100.0 weight got id 7
> Reassigned 1024 (100.00%) partitions. Balance is now 33.07.
> -------------------------------------------------------------------------------
> NOTE: Balance of 33.07 indicates you should push this
>      ring, wait at least 1 hours, and rebalance/repush.
> -------------------------------------------------------------------------------
> 
> Any idea why the balance is 33.07 rather than 0?
> 
> I've tried using a partition power of 18 but get the same result
> (balance of 33.33 with 262144 partitions).
> 
> I'm using Swift 1.8.0-rc1.
> 
> Thanks
> Adrian
> 
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