Hi Neil-
I just spent two months and rewrote all of nfs(5). It should appear
in the next release of nfs-utils. Steve, when can we expect to see
the updated man page?
On Jan 3, 2008, at 9:32 PM, Neil Brown wrote:
>
> I've been trying to understand exactly how timeouts work in the NFS
> client and find that the man page in nfs-utils is not correct.
>
> In particular, the implementation differentiates between TCP and UDP,
> while the man page does not make that distinction.
>
> I have attempted an update to the man page as you can see below. It
> is entirely possible that I have not got it completely correct (or
> comprehensible) so I'm asking for people to check that what I have
> written is correct and clear.
>
> This I would particularly like comment on:
>
> 1/ I have left
>
> Better overall performance may be achieved by increasing the
> timeout when mounting on a busy network, to a slow server, or through
> several routers or gateways.
>
> unchanged. Is it still a reasonable thing to say?
>
> 2/ I have moved the documentation about major timeouts into the
> retrans=
> section. Does that break the description up too much?
>
> 3/ the old text seems to say that after the first major-timeout, a
> slightly different sequence of timeouts are used. I couldn't find
> evidence of this in the code. Did I miss something, or is my text
> correct?
>
> 4/ Did this change in some ancient kernel version, and should the
> version number of the change be documented? e.g. is it a 2.4 / 2.6
> difference?
>
> 5/ As the behaviour is quite different for UDP and TCP, should we
> introduce a major_timeo= option which calculates an appropriate
> retrans= based on the actual timeo= and proto= used.
>
> and anything else that occurs to anyone.
>
> Thanks,
> NeilBrown
>
> diff --git a/utils/mount/nfs.man b/utils/mount/nfs.man
> index d92da19..0142075 100644
> --- a/utils/mount/nfs.man
> +++ b/utils/mount/nfs.man
> @@ -83,24 +83,50 @@ Note: Setting this size to a value less than
> the largest supported
> block size will adversely affect performance.
> .TP 1.5i
> .I timeo=n
> -The value in tenths of a second before sending the
> -first retransmission after an RPC timeout.
> -The default value is 7 tenths of a second. After the first timeout,
> -the timeout is doubled after each successive timeout until a maximum
> -timeout of 60 seconds is reached or the enough retransmissions
> -have occured to cause a major timeout. Then, if the filesystem
> -is hard mounted, each new timeout cascade restarts at twice the
> -initial value of the previous cascade, again doubling at each
> -retransmission. The maximum timeout is always 60 seconds.
> +The value in tenths of a second for the first RPC timeout. If no
> +reply has been received in this much time, the message is
> +retransmitted.
> +Further timeouts are handled differently depending on the connection
> +type.
> +
> +For UDP (which is unreliable and lacks congestion control),
> +each successive timeout is twice the previous timeout. As the
> default
> +is 11 tenths of a seconds, the timeouts used if
> +.I timeo=
> +is not specified are 1.1, 2.2, 4.4, 8.8,... seconds. The timeout for
> +each retransmission is limited to 60 seconds, so the next few numbers
> +in the above sequence would be 17.6, 35.2, 60, 60.
> +
> +For reliable protocols such as TCP and RDMA, the successive timeouts
> +grow linearly rather than exponentially to a maximum of 10 minutes.
> +The default is 1 minute, so the default successive timeout are 1,
> +2, 3, 4, 5, 6, 7, 8, 9, 10, 10, 10 minutes.
> +
> +It is unwise to set
> +.I timeo=
> +explicitly without also setting the protocol to use, as it has a
> +significantly different effect depending on protocol.
> +
> Better overall performance may be achieved by increasing the
> timeout when mounting on a busy network, to a slow server, or through
> several routers or gateways.
> .TP 1.5i
> .I retrans=n
> The number of minor timeouts and retransmissions that must occur
> before
> -a major timeout occurs. The default is 3 timeouts. When a major
> timeout
> -occurs, the file operation is either aborted or a "server not
> responding"
> -message is printed on the console.
> +a major timeout occurs. The default is 2 yielding a total of 3
> +attempts (1 transmission and 2 retransmissions). When a major
> timeout
> +occurs the behaviour depends on whether the filesystem was mounted
> +.I hard
> +or
> +.IR soft .
> +In the case of a
> +.I soft
> +mount, the operation will abort and typically return an IO error to
> +the application. In the case of a
> +.I hard
> +mount a "server not responding" message will be printed on the
> +console, and the request will be retried with the original series of
> +timeouts.
> .TP 1.5i
> .I acregmin=n
> The minimum time in seconds that attributes of a regular file should
> -
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--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
Chuck Lever wrote:
> Hi Neil-
>
> I just spent two months and rewrote all of nfs(5). It should appear in
> the next release of nfs-utils. Steve, when can we expect to see the
> updated man page?
I committed the update a few days ago...
steved.