NFS write() calls lead to read() calls?

[Ivan Voras]

Ulrich Spoerlein wrote:

> If I run the scp again, I can see X MB/s going out from HostA, 2*X
> MB/s coming in on HostB and X MB/s out plus X MB/s in on HostC. What's
> happening is, that HostB issues one NFS READ call for every WRITE
> call. The traffic flows like this:
> 
>  ----->   ----->
> A        B        C
>           <-----
> 

> The real weirdness comes into play, when I simply cp(1) from HostB
> itself like this:
> 
> hostB # cp 500MB /net/share/
> 
> I can do this over and over again, and _never_ get any noteworthy
> amount of NFS READ calls, only WRITE. The network traffic is also, as
> you would expect.

Have you tested with a small C program or a script to see if it's the 
rewriting that's causing reads or is it some weird artifact of scp?

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