# [OmniOS-discuss] Slow NFS speeds at rsize > 128k

Dan McDonald danmcd at omniti.com
Wed Jan 7 15:12:45 UTC 2015

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    > On Jan 7, 2015, at 5:28 AM, Stephan Budach <stephan.budach at JVM.DE> wrote:
    >
    > Hello everyone,
    >
    > I am sharing my zfs via NFS to a couple of OVM nodes. I noticed really bad NFS read performance, when rsize goes beyond 128k, whereas the performance is just fine at 32k. The issue is, that the ovs-agent, which is performing the actual mount, doesn't accept or pass any NFS mount options to the NFS server. To give some numbers, a rsize of 1mb results in a read throughput of approx. 2Mb/s, whereas a rsize of 32k gives me 110Mb/s. Mounting a NFS export from a OEL 6u4 box has no issues with this, as the read speeds from this export are 108+MB/s regardles of the rsize of the NFS mount.
    >
    > The OmniOS box is currently connected to a 10GbE port at our core 6509, but the NFS client is connected through a 1GbE port only. MTU is at 1500 and can currently not be upped.
    > Anyone having a tip, why a rsize of 64k+ will result in such a performance drop?

    Assuming you're running over TCP, perhaps you need to increase the receive window?

    	ndd -set /dev/tcp tcp_xmit_hiwat 1048576

    Dan

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