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    SubjectHow to monitor Linux NFS client load?
    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!

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      Last update: 2009-07-11 19:05    [W:0.021 / U:53.864 seconds]
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