Re: Text based mount options ignoring the preferred rwsize?

James Pearson
2009-09-09T21:47:05Z

Chuck Lever wrote:
>>
>> Should the kernel be setting rsize (and wsize) to 0 by default?
>
>
> nfs(5) says:
>
> "If an [rw]size value is not specified, or if the specified [rw]size
> value is larger than the maximum that either client or server can
> support, the client and server negotiate the largest [rw]size value
> that they can both support."
>
> So the text-based behavior is what is documented now.
>
> Does anyone know of a reason to use the server's "preferred" transfer
> size rather than the largest size supported by both client and server?
> Usually those are the same.

In this case, the manufacturer of the NFS server recommends using 128Kb
for rsize and 512Kb for wsize - although the maximum rsize it supports
is 512Kb. I assume in their testing, these values have given optimal
performance figures.

The default behaviour with binary mount options when no [rw]size is to
select these preferred values - which to me, makes sense - as by not
giving a [rw]size, you are leaving it up the server to pick the 'best'
values for you - which I guess in most (all other?) cases happen to be
the maximum size.

James Pearson