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    SubjectRe: effect of nfs blocksize on I/O ?
    On Mon, Sep 29, 2003 at 12:19:30AM -0700, Trond Myklebust wrote:
    > >>>>> " " == Frank Cusack <> 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) */

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