When a proxy-server executes multiple COPY requests, its network interface bandwidth can easily saturate in case of replica policy. For an EC policy, it can consume a lot of CPU power.
Example: with a 10Gbps NIC and a 3-replica policy, reading at 1Gbps, writing at 3Gbps, only 3 COPY can happens at the same time without contention.
The object copy could take place directly between object-servers. I guess there is generally more network capacity at object-servers than at proxy-servers.
For replica policy, each replica could be copied to the corresponding object-server. For EC policy, each fragment could be copied to the corresponding object-server
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