Slow NFS writes with sec=krb5

Florian Oppermann florian.oppermann at itp.uni-hannover.de
Wed Oct 7 14:23:45 UTC 2015


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Ok, we kind of resolved the issue: For strange reasons unknown to us
our predecessors used a separate keytab for the nfs/… kerberos
principal and modified the line

> exec rpc.gssd

in /etc/init/gssd.conf to

> exec rpc.gssd -t 30 -k /etc/krb5.nfs.keytab

After merging the keytabs and restoring the original line the NFS
mount is fast for current kernel versions.

We still don’t know why this slowed down the connection but it works now
…

Best regards,
Florian

On 07.10.2015 11:51, Florian Oppermann wrote:
> Sorry for talking to myself…
> 
>> 1) On one slow machine that is running precise I booted into an 
>> old kernel image (3.2 instead of 3.13). The behaviour was the 
>> expected: The kerberized automount got fast write speeds.
>> Booting back to 3.13 made it slow again.
> 
> I expanded this test scenario on one of our trusty machines and 
> installed some old kernel versions: From 3.2 to 3.11.10.15 the NFS 
> mount was fast, it got slow at version 3.12.0rc1 (last two
> packages for saucy). (Note: I refer to the packages from 
> <http://kernel.ubuntu.com/~kernel-ppa/mainline/>.)
> 
> Maybe someone with more knowledge about NFS or kernel development 
> could have a look at the changelog 
> (<http://kernel.ubuntu.com/~kernel-ppa/mainline/v3.12-rc1-saucy/CHANGE
S>
>
> 
).
> I believe some change there has undesired effects in certain
> environment s.
> 
> Best regards, Florian
> 
> On 05.10.2015 18:14, Florian Oppermann wrote:
>> On 05.10.2015 17:25, Brandon Vincent wrote:
>>> There was an issue with the system detecting if gssd was 
>>> running, so my only recommendation to you is to update to the 
>>> latest kernel and NFS/Kerberos related packages and see if
>>> that resolves your issue.
> 
>> I just tried the following things:
> 
>> 1) On one slow machine that is running precise I booted into an 
>> old kernel image (3.2 instead of 3.13). The behaviour was the 
>> expected: The kerberized automount got fast write speeds.
>> Booting back to 3.13 made it slow again.
> 
>> I think this rules out the possibility that some other packages 
>> have broken something and should be upgraded.
> 
>> 2) On one of our trusty machines I installed the .debs for 4.0.0,
>>  4.1.0, 4.2.3 and 4.3.0 from 
>> <http://kernel.ubuntu.com/~kernel-ppa/mainline/>. None of the new
>>  kernels enabled the fast kerberized NFS automount.
> 
>> I suspected them to solve the issue because my laptop with Debian
>>  testing had fine write performance. I have to check the kernel 
>> version though.
> 
>> Maybe we’ll just try to setup one machine with a clean 15.10
>> when it’s released.
> 
>> Best regards, Florian
> 
> 
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