On 08/29/2018 02:33 AM, Test Test wrote:
Hi cephers: Recently, I was testing the multisite of rgw(ceph 12.2.5). I have some questions, can you give me a hand? 1. every zone has its own placement-rules. But when I create a bucket, it will be created on all the other zones which requires the zone s have the same placement-rule. So are the placement rules the zone's info or the zonegroup's info?
the set of possible placement rules are defined in the zonegroup. each zone needs to map each of those placement rules to its own pool names. so there's both a global (zonegroup) part and a local (zone) part
2. every bucket records its placement-rule and it asks the placement-rule never changed. But we can change the placement-rule easily. So why does not the bucket record the pool's info instead of the placement-rule?
all bucket metadata (which includes this placement id) is replicated between zones by metadata sync, so is effectively global. the pool names themselves are local to zones, because different zones want to use different pools. that wouldn't work if the bucket stored the pool names directly
in fact, before jewel the bucket did store pool names - and we still support the 'explicit_placement' field for backward compatibility, though it has that defect when used in a multisite configuration
3. the zonegroup has a default placement-rule. Why is the default placement-rule zonegroup-level, not zone-level? Thanks!!!
the default placement rule is used when creating new buckets, and all bucket creation happens on the metadata master zone (the master zone of the master zonegroup). if that zone becomes unavailable and you fail over to another master zone, it should use that same default
