Angelescu, Silviu (NetApp) wrote:
Someone mentioned below "With C-mode there's "local" and "remote" array access". Actually, "remote" access would never happen when LIFs are configured on each node (which is the recommended best practice configuration).
That someone was me. If you consider an NFSv3 based (not NFSv4 with referrals or v4.1 with pNFS extension) environment with many 100s of NFS clients and they have > 100 NFS mounts each to various places in the GNS from the C-mode cluster, and they cannot really ever be restarted all at once except under exceptional circumstances (meaning: re-mount happens very rarely for a large portion of the data...)
Even if LIFs are configured on each node, as soon as you move things around in the back-end, you'll get lots of cross Cluster Network accesses. It's pretty much unavoidable the way I see things
The only case when you'd get remote traffic thru the interconnect 10GigE network is when you need to shutdown a node for an upgrade for example, or when you move a volume to a node where you don't have a LIF configured (but you could also move the LIF along with the volume or just create a new LIF on the destination node and that would provide a direct path to the new destination node for the volume; one LIF on each node is the bottom line recommended best practice).
That's fine but in the above scenario i described it won't really help that much
Regarding the "performance impact" of cluster-mode, you may want to check the latest SPC-1 benchmark results with FAS 6240 in cluster-mode: http://www.storageperformance.org/benchmark_results_files/SPC-1/NetApp/A001 15_NetApp_FAS6240-cluster/a00115_NetApp_FAS6240-cluster_SPC-1_executive-sum mary.pdf
It's a nice result, comparable to any other major "Tier 1" Block Storage vendor out there
The latency impact of C-mode compared to 7-mode cannot be juged from that data though, simply because there's no published SPC-1 benchmark for a 7-mode "single node" (or HA cluster) FAS6240. If there were, then I would absolutely do that comparison for FC Block Storage use case as well, not just SPECsfs2008
Regards, /M