missing error message when rebalancing a ring with more replicas than available zones

[Christian Berendt]

I think it should be checked if replicas <= zones before starting the rebalancing and then there should be printed a correct error message.

os0020:/etc/swift # swift-ring-builder account.builder create 18 3 1

os0020:/etc/swift # swift-ring-builder account.builder
account.builder, build version 2
262144 partitions, 3 replicas, 2 zones, 2 devices, 100.00 balance
The minimum number of hours before a partition can be reassigned is 1
Devices: id zone ip address port name weight partitions balance meta
             0 1 172.19.13.30 6002 xvdb1 100.00 0 -100.00
             1 2 172.19.13.31 6002 xvdb1 100.00 0 -100.00

os0020:/etc/swift # swift-ring-builder account.builder rebalance
Traceback (most recent call last):
  File "/usr/bin/swift-ring-builder", line 690, in <module>
    Commands.__dict__.get(command, Commands.unknown)()
  File "/usr/bin/swift-ring-builder", line 528, in rebalance
    parts, balance = builder.rebalance()
  File "/usr/lib64/python2.6/site-packages/swift/common/ring/builder.py", line 254, in rebalance
    self._initial_balance()
  File "/usr/lib64/python2.6/site-packages/swift/common/ring/builder.py", line 412, in _initial_balance
    while available_devs[index]['zone'] in other_zones:
IndexError: list index out of range

[Samuel Merritt (torgomatic)]

FYI, there's a pending patchset (https://review.openstack.org/6845) that, if it gets accepted, would fix this by removing the zones >= replicas restriction.

[Andy McCrae (andrew-mccrae)]

Thanks for the heads up! I've had a look at the pending patchset, I like the change, will hold onto this until the patchset is merged and then confirm/close it out.

[Andy McCrae (andrew-mccrae)]

Confirmed this was fixed in the release mentioned by Samuel above:

root@swiftTest:/etc/swift# swift-ring-builder test.builder rebalance
Reassigned 256 (100.00%) partitions. Balance is now 0.00.
root@swiftTest:/etc/swift# swift-ring-builder test.builder
test.builder, build version 2
256 partitions, 3 replicas, 1 zones, 2 devices, 0.00 balance

Won't error when zones < replicas and now approaches it in a more sensible manner. Marking this as Resolved.