Hi, We are currently using 2 OSD hosts with SSDs to provide RBD backed volumes for KVM hypervisors. This 'cluster' is currently set up in 'Location A'.
We are looking to move our hypervisors/VMs over to a new location, and will have a 1Gbit link between the two datacenters. We can run Layer 2 over the link, and it should have ~10ms of latency. Call the new datacenter 'Location B'. One proposed solution for the migration is to set up new RBD hosts in the new location, set up a new pool, and move the VM volumes to it. The potential issue with this solution is that we can end up in a scenario where the VM is running on a hypervisor in 'Location A', but writing/reading to a volume in 'Location B'. My question is: what kind of performance impact should we expect when reading/writing over a link with ~10ms of latency? Will it bring I/O intensive operations (like databases) to a halt, or will it be 'tolerable' for a short period (a few days). Most of the VMs are running database backed e-commerce sites. My expectation is that 10ms for every I/O operation will cause a significant impact, but we wanted to verify that before ruling it out as a solution. We will also be doing some internal testing of course. I appreciate any feedback the community has. - Logan
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