Re: NFS caching problem

[Peter Staubach <staubach@redhat.com>]

David Warren wrote:

> I have discovered a wierd problem with NFSv3 on linux.
> I have 3 machines
> machine A and B  both mount a disk D  from machine C
> The options are tcp,rw,hard and intr.
>
> Program test runs on machine A writing to D:
> (fortran)
>      program test
>      do i=1,10
>         call system("/bin/rm t")
>         open (10, file='t', status='new')
>         write(10,*)i
>         write(6,*)i
>         close(10)
>         call sleep(1)
>      enddo
>      end
>
> program t2 runs on machine B reading from D:
> (c, but doesn't have to be)
> #include <stdlib.h>
> #include <fcntl.h>
> main(){
>  char in[80];
>  int file;
>  int len;
>
>  while(1){
>    file=open("t", O_RDONLY);
>    len=read(file,in,79);
>    in[len]='\0';
>    printf("%s\n",in);
>    close(file);
>  }
> }
>
> while machine A is counting 1 - 10 and placing these numbers into file 
> t, machine B is continually reading 1 from file t, then after a while 
> it will switch to another number and read it for a while. In my first 
> version of this, I was opening and rewriting the same file. In that 
> version, machine B always read 1's. Now that I am creating new inodes 
> all the time, it changes every few minutes while I repeatedly rerun 
> test on machine A.
>
> Now for the other interresting facts:
> Reading this file from an unrelated sun during this produces the same 
> result as machine B.
> The same thing under NFSv4 does not do this. It works exactly as one 
> would expect it to. As soon as the file is writen, the reader sees the 
> new data.
>
> Any ideas what I could have done wrong in my NFSv3 set up? Is there 
> some kernel parameter that need tweaking? is there some mount option I 
> should have??? 


What version(s) of Linux are on machines, A, B, C?  What is the local file
system on machine, C, which is on disk, D?

    Thanx...

       ps


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