From: Chuck Lever <chuck.lever@oracle.com>
To: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Max Matveev <makc@redhat.com>, linux-nfs@vger.kernel.org
Subject: Re: NFS/TCP timeout sequence
Date: Thu, 7 Jul 2011 10:04:47 -0400 [thread overview]
Message-ID: <5F749FAD-94B0-4D9D-84F6-F7D9662A1CF6@oracle.com> (raw)
In-Reply-To: <1310046439.3863.30.camel@lade.trondhjem.org>
On Jul 7, 2011, at 9:47 AM, Trond Myklebust wrote:
> On Thu, 2011-07-07 at 18:11 +1000, Max Matveev wrote:
>> I've had to look at the way NFS/TCP does its timeouts and backoff
>> and it does not make a lot of sense to me: according to the
>> following paragram from nfs(5) on Fedora 14 (I'm using Fedora 14
>> because it has more text then the same page in nfs-utils):
>>
>> timeo=n The time (in tenths of a second) the NFS client waits
>> for a response before it retries an NFS request. If this
>> option is not specified, requests are retried every 60
>> seconds for NFS over TCP. The NFS client does not per‐
>> form any kind of timeout backoff for NFS over TCP.
>>
>> but if I try the mount with timeo=20,retrans=7 then I'm getting
>> retransmits which are 2, 4, 6, 8, 2, 4, 6, 8 seconds apart, i.e.
>> there is a) linear backoff and b) the backoff is not long enough to
>> let the complete sequence of 7 retransmits run its course.
>
> Sigh... Firstly, 2 second timeouts are complete lunacy when using a
> protocol that guarantees reliable delivery, such as TCP does. Anyone who
> tries it deserves exactly what they get: poor unreliable performance.
We shouldn't allow such low settings.
> Secondly, the _other_ fix for this problem is to fix the documentation.
How is the documentation incorrect? We do not want any kind of back-off for stream transports.
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
next prev parent reply other threads:[~2011-07-07 14:05 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-07-07 8:11 NFS/TCP timeout sequence Max Matveev
2011-07-07 13:47 ` Trond Myklebust
2011-07-07 14:04 ` Chuck Lever [this message]
2011-07-07 14:16 ` Trond Myklebust
2011-07-07 14:44 ` Chuck Lever
2011-07-07 14:59 ` Trond Myklebust
2011-08-04 5:54 ` Max Matveev
2011-08-04 5:42 ` [PATCH] NFS: allow enough time for timeouts to run Max Matveev
2011-08-04 5:47 ` [PATCH] Update nfs(5) manpage - timeo for NFS/TCP Max Matveev
2011-08-04 12:04 ` Jim Rees
2011-08-05 0:57 ` Max Matveev
2011-08-05 1:39 ` Jim Rees
2011-08-05 2:14 ` Max Matveev
2011-07-08 6:05 ` NFS/TCP timeout sequence Max Matveev
2011-07-08 0:20 ` Max Matveev
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