Re: "Using NFS over UDP on high-speed links such as Gigabit can cause silent data corruption."

[Chuck Lever <chuck.lever@oracle.com>]

On Mar 4, 2012, at 9:17 PM, Harshula wrote:

> On Tue, 2012-02-28 at 10:50 -0500, Chuck Lever wrote:
>> On Feb 28, 2012, at 9:35 AM, Chuck Lever wrote:
> 
>>> My comment is that if the text in the TRANSPORT METHODS section in
>> nfs(5) about UDP reassembly is not adequate it should be updated.  I
>> would rather see the meat of the proposed text merged into that
>> section; otherwise we have two disparate sections discussing the same
>> topic.  That section is where this kind of discussion belongs.
> 
> Good point. I'll try to massage the text into that section.

Thanks.

>> A few more comments.
>> 
>> Any file, including a /proc file, called out in new text should be
>> added to the FILES section, IMO.
>> 
>> If we can't resolve the provenance issue, someone could rewrite the
>> patch from scratch so that it addresses the review comments.
> 
> We now know who authored (Olaf Kirch) and committed (Mads Martin
> Joergensen) the text at SUSE. Do we need to get a sign-off from someone
> at SUSE?

IMO if Olaf is still there, he can send a SOB.  But IANAL.

>> I don't agree with adding in-code warnings.  Mount works silently
>> unless it fails, and this is not a mount failure.  Would such warnings
>> ever be seen for NFS mounts added to /etc/fstab, or performed by
>> automounter?  I think by and large most people type "mount -t nfs"
>> without options and will get our current default transport setting,
>> which is TCP, or UDP if the server does not support TCP.  Isn't that
>> adequate?
>> 
>> We also know that the risk of using UDP is mitigated by using jumbo
>> frames, specifying a small r/wsize, or by reducing the fragment
>> reassembly timeout.  If an admin does those things, she still gets the
>> warning.
>> 
>> It seems needlessly alarmist, and useless for our most common use
>> cases.
> 
> Sounds reasonable. Just the man page text then.

-- 
Chuck Lever
chuck[dot]lever[at]oracle[dot]com