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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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