[Python-talk] NFS trickery and deceit

[Bruce Labitt]

Ric Werme wrote:
>> I have a blade processor that has no local file system.  The file system
>> for the blade is provided by NFS on my local ubuntu workstation.  This is
>> the general program flow:
>>
>> 1. My python program on the workstation creates a datafile on the
>> workstation for the remote blade to process.
>> 2. The blade processes the input file and creates an output file.  I just
>> managed to get this to work using paramiko.  So the blade has to transfer
>> the data from NFS to local memory, process it and send it back from its
>> local memory back to NFS, which is on the ubuntu box.
>> 3. My python program then reads the file and displays the surface generated
>> by the blade.
>>
>> Since the files are all on my ubuntu box, I'd like to minimize the gbit
>> network traffic to and from the blade.  I would think that the python step
>> 3 file read would not have to be done through paramiko to the blade, but
>> rather directly from the /srv/nfsroot/stuff directory on my ubuntu box.
>>     
>
> Well, you could unplug the blade server and do all three steps on your
> workstation.  I'll assume there's a good reason for doing step 2 on the
> blade server.  There should be no problem executing step 3 on your
> workstation.  NFS V3 does have a few "features" that can cause some
> grief with local file system caches, however in your case "close-to-open"
> consistency should handle that.  Basically, when the blade closes the file
> that should force the kernel to send over all the data to the workstation,
> and then when you open the file on the workstation you shold be all set.
> (On a different client, the open should force checking with the server to
> see if the file changes, and even that should work.)
>
> NFS locking is only important if two clients both have the file open and
> are modifying it.
>
>    -Ric Werme
>   
The good reason for step 2, is that the blade is  > 150x faster than the 
fastest server I have benchmarked.  Stuff that would take weeks takes an 
hour or so.

So it sounds like things are going to work... :)