Re: Text based mount options ignoring the preferred rwsize?

Chuck Lever
2009-09-09T19:23:45Z

On Sep 8, 2009, at 12:47 PM, James Pearson wrote:
> I've noticed a difference in the rsize used when mounting a file
> system between using text and binary mount options.
>
> The client is running a CentOS5 based distro with a 2.6.32-rc8 kernel
>
> The server has a preferred rsize of 128kb and maximum rsize of 512kb
>
> When I use mount.nfs from CentOS5/RHEL5 nfs-utils (based on v1.0.9)
> and don't give any rsize option, it mounts the file system with a
> rsize of 128kb. This uses binary mount options
>
> But, when using mount.nfs from nfs-utils 1.2.0, the file system is
> mounted with an rsize of 512kb
>
> Looking at the nfs-utils and kernel source, it appears that for
> binary options, rsize is set to 0 if not given by mount.nfs, and the
> kernel eventually, in this case, increases this to preferred size.
>
> But for text mount options, if not set by mount.nfs, the default
> size is set to NFS_MAX_FILE_IO_SIZE in the kernel, which, in this
> case, gets reduced to the server maximum size.
>
> 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.

> Thanks
>
> James Pearson
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--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com