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I've been noticing somethings strange with my RGW federation. I
added some statistics to radosgw-agent to try and get some insight
(https://github.com/ceph/radosgw-agent/pull/7), but that just showed
me that I don't understand how replication works. When PUT traffic was relatively slow to the master zone, replication had no issues keeping up. Now I'm trying to cause replication to fall behind, by deliberately exceeding the amount of bandwidth between the two zones (they're in different datacenters). Instead of falling behind, both the radosgw-agent logs and the stats I added say that slave zone is keeping up. But some of the numbers don't add up. I'm not using enough bandwidth between the two facilities, and I'm not using enough disk space in the slave zone. The disk usage in the slave zone continues to fall further and further behind the master. Despite this, I'm always able to download objects from both zones. How does radosgw-agent actually replicate metadata and data? Does radosgw-agent actually copy all the bytes, or does it create placeholders in the slave zone? If radosgw-agent is creating placeholders in the slave zone, and radosgw populates the placeholder in the background, then that would explain the behavior I'm seeing. If this is true, how can I tell if replication is keeping up? -- |
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