read and write size in NFS v4

[Yong Huang]

> From: "Stephen Carville" <stephen.carville at gmail.com>
> Subject: read and write size in NFS v4
> To: "General Red Hat Linux discussion list" <redhat-list at redhat.com>
> 
> I am migrating my NFS file server from RHEL3 to RHEL5 and moving up to
> NFS v4 where i can.  Once question I still have is what is the maximum
> rsize and wsize i can set for V4 automount?  The file
> include/linux/nfsd/const.h says teh maximum is 32*1024 (32K) but some
> google postings claim that does not apply to V4;  I've tried v4
> automounts with values up to 1048576 and none of the machine have
> complained.
> 
> A part of the new server's duties will be to accept the RMAN (oracle)
> backups so speed is important.  I am using a dedicated gigabit switch
> with jumbo frames (9000 bytes) and I have tuned the TCP  for the
> "private" interfaces on all the connected interfaces.  These is the
> only parameter I am not sure what I can get away with.  I have it set
> to 32768 for the current v3 setup.
> 
> -- 
> Stephen Carville

I don't know the answer. But can you check nfsstat to see what it says the size
is? Also, strace some read and write operations and see what the return values
for read() and write() are. But I guess the latter method may not tell us the
underlined driver level chunk size.

Yong Huang