Optimising NFS for system files

[Peter Boosten]

On 31 dec 2008, at 08:53, Bernard Dugas <bernard at dugas-family.org>  
wrote:

> Wojciech Puchar wrote:
>
>>> nfsserver# time tar -cf - clientusr-amd64 > /dev/null
>>> 5.001u 12.147s 1:23.92 20.4%    69+1369k 163345+0io 0pf+0w
>>>
>>> client9# time tar -cf - /usr > /dev/null
>>> tar: Removing leading '/' from member names
>>> 3.985u 19.779s 4:32.47 8.7%     74+1457k 0+0io 0pf+0w
>>>
>>> Note : clientusr-amd64 is around 1.3GB and is the same directory  
>>> exported to client9 /usr with nfs.
>>>
>> it's FAST. what's wrong?
>
> First thing that may be wrong is the understanding of the time  
> figures. The documentation is not clear about them and the -h option  
> is not working :
>
> client6# time -h tar -cf - /usr > /dev/null
> -h: Command not found.
> 0.000u 0.000s 0:00.00 0.0%      0+0k 0+0io 0pf+0w
>
> The main thing is that the 3rd figures 1:23.92 and 4:32.47 seems to  
> be the time i wait in front of the computer while it works (ok, i  
> know, i should enjoy a beer, or hot coffee with this nice snow ;-) :
>
> client9# date ; time tar -cf - /usr > /dev/null ; date ;
> Wed Dec 31 08:23:59 CET 2008
> tar: Removing leading '/' from member names
> 4.103u 19.651s 4:25.80 8.9%     74+1453k 0+0io 2pf+0w
> Wed Dec 31 08:28:25 CET 2008
>
> and 08:28:25 - 08:23:59 = 00:04:26 is very close to 4:25.80.
>
> On server, it means : 1440MB / 84s = 17MB/s
> On client, that becomes : 1440MB / 266s = 5.4MB/s
>
> I know the disk is not very fast, but i would like the NFS layer not  
> to add too much...
>
> I don't want my users to wait between 3 or 4 times more because  
> computer is using NFS.

In my opinion there are more considerations than only nfs: the data is  
pulled twice over the network, and the tar process might initiate  
paging which is done over the network as well. The tar comparison is  
not a good one.

Peter
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