On Jun 22, 2010, at 11:44 AM, Alex Still <alex.ranskis at gmail.com> wrote: > [...] > >>> On some servers this behavior returned despite rsize being set to 32k, >>> I had to set it to 8k to get reasonnable throughput. So there's >>> definitly something fishy going on. This has been reported on over 20 >>> machines, so I don't think it's faulty hardware we're seeing. >>> >>> Any thoughts, ideas on how to debug this ? >> >> Can you explain the network environment and the connectivity between the client and server some more. > > Clients are blade servers. The blade chassis have integrated cisco > switches, which are plugged to a cisco 6509. The NFS server is on > another site 40km away, directly connected to another 6509. These > datacenters are linked via DWDM. > Latency between a client and the NFS server is about half a > millisecond. Jumbo frames are enabled. > > Blades have 1 Gb link > The NFS server has multiple 1Gb links, used for different shares > Neither are close to full utilization, maybe 100Mb/s of traffic and 20 > 000 paquets/s at the server end I have seen non-standard jumbo frames cause problems in the past. Can you try unmounting shares on one client, setting the MTU to 1500, re-mount the shares and see how it works? TCP between server and client will negotiate down to client's MSS so no need to change server's MTU. -Ross