On 08/30/2018 08:38 PM, Test Test wrote:
Casey Bodley <cbodley@xxxxxxxxxx> 于2018年8月29日周三 下午8:24写道：
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
The list of placement-rules is global and the content of
placement-rules is local. After a bucket uses the placement-rule, the
placement-rule should not be changed again. If we modify as follows:
1. When a bucket is created, it records the placement-rule and pools'
info( in 'explicit_placement').
2. When a bucket syncs, the plcament-rule syncs, the pools' info does
not sync. the bucket in other zones updates its pools‘ info (according
the placement-rule in other zones).
So the bucket in different zones will have the same placement-rule but
different pools' info. And changing the placement-rule will not affect
the availability of the bucket.
is there any mechanism that changes a bucket's placement rule after
creation?
i think we'll want to build on storage classes to do anything more
complicated, like per-object placement, lifecycle transitions, etc
