Re: effect of nfs blocksize on I/O ?

[Frank Cusack <fcusack@fcusack.com>]

On Mon, Sep 29, 2003 at 12:19:30AM -0700, Trond Myklebust wrote:
> >>>>> " " == Frank Cusack <fcusack@fcusack.com> writes:
> 
>      > 2.6 sets this to nfs_fsinfo.wtmult?nfs_fsinfo.wtmult:512 = 512
>      >     typically.
> 
>      > (My estimation of "typical" may be way off though.)
> 
>      > At a 512 byte blocksize, this overflows struct statfs for fs >
>      > 1TB.  Most of my NFS filesystems (on netapp) are larger than
>      > that.
> 
> Then you should use statfs64()/statvfs64(). Nobody is going to
> guarantee to you that the equivalent 32-bit syscalls will hold for
> arbitrary disk sizes.

I see.

> OTOH, bsize is of informational interest to programs that wish to
> optimize I/O throughput by grouping their data into appropriately
> sized records.

So then isn't the optimal record size 8192 for r/wsize=8192?  Since the
data is going to be grouped into 8192-byte reads and writes over the wire,
shouldn't bsize match that?  Why should I make 16x 512-byte write() syscalls
(if "optimal" I/O size is bsize=512) instead of 1x 8192-byte syscall?

SUSv3 says:

    unsigned long f_bsize    File system block size. 
    unsigned long f_frsize   Fundamental file system block size.

Solaris statvfs(2) says:

    u_long      f_bsize;             /* preferred file system block size */
    u_long      f_frsize;            /* fundamental filesystem block
                                         (size if supported) */

/fc