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From "James A. Robinson" <>
Subject Re: NFS v4 locks "given up" w/o any logging?
Date Mon, 21 Mar 2016 22:46:57 GMT
I suppose I should pose the question to folks that use NFS, do you use TCP
or UDP for your NFS stack?

On Mon, Mar 21, 2016 at 3:29 PM James A. Robinson <>

> Running a packet trace while the problem was occurring let me see that the
> problem is that the NFS layer isn't even being involved for 3 minutes due
> to the TCP layer retrying for 3 minute before notifying the caller of the
> error.
> The client sends SYN packets, doesn't get an ACK, and finally times out
> after 3 minutes.  The documentation for Linux (the client in this case)
> indicates the following default:
> tcp_syn_retries (integer; default: 5; since Linux 2.2)
>               The maximum number of times initial SYNs for an active TCP
>               connection attempt will be retransmitted.  This value should
>               not be higher than 255.  The default value is 5, which
>               corresponds to approximately 180 seconds.
> I think this means that it's not possible to get faster failover w/o
> modifying the default values for the TCP layer.  This particular error is
> always going to take at least 3 minutes to surface.
> Jim

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