We've run into issues with the number of open TCP connections from a single client to the OSDs in our Ceph cluster.
We can (& have) increased the open file limit to work around this, but we're looking to understand what determines the number of open connections maintained between a client and a particular OSD. Our naive assumption was 1 open TCP connection per OSD or per port made available by the Ceph node. There are many more than this, presumably to allow parallel connections, because we see 1-4 connections from each client per open port on a Ceph node.
Here is some background on our cluster:
* still running Firefly 0.80.8
* 414 OSDs, 35 nodes, one massive pool
* clients are KVM processes, accessing Ceph RBD images using virtio
* total number of open TCP connections from one client to all nodes between 500-1000
Is there any way to either know or cap the maximum number of connections we should expect?
I can provide more info as required. I've done some searches and found references to "huge number of TCP connections" but nothing concrete to tell me how to predict how that scales.
Thanks,
Rick
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