Recently we have the case of very high latencies on NFS reads as reported by application (SAP R/3). NFS server was NetApp FAS; according to NetApp statistic, average volume read latencies were in order 10ms, while SAP stats gave 30-50ms. Systems were interconnected by dedicated 1Gb/s Cisco switches (3750G) with ca. 30% max load on interfaces. On advice of my colleague we changed sunrpc.tcp_slot_table_entries from default 16 to 128 which seemed to make situation much better - without changing load pattern of filer in any visible way. Now, I can understand, why we observed much higher latency on system and why changing (what effectively is) queue depth helped. But I am totally frustrated that there does not appear to be *any* possibility to detect this situation on Linux side and to get a real numbers of real NFS IO latencies or number of requests waiting to be executed (and I do not even dream about per-mount point stats). I am grateful for any hints how can we monitor Linux NFS client and get real-life numbers of what happens inside. Thank you! -andrey
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