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Re: Network file transfer rate comparisons

    Date: Fri, 27 Jan 89 09:17 EST
    From: Hornig@ALDERAAN.SCRC.Symbolics.COM (Charles Hornig)

	Date: Thu, 26 Jan 89 21:44 EST
	From: Moon@STONY-BROOK.SCRC.Symbolics.COM (David A. Moon)

	Just to set the record straight, based on my knowledge of the underlying
	disk hardware and software:

    I'll add my two cents as well.

	    Date: Thu, 26 Jan 89 15:29 EST
	    From: miller@CS.ROCHESTER.EDU (Brad Miller)
	    Note that 3670s have a much faster SMD access time than the 50. Part of the
	    reason is software, part of the reason is that the channel is 16 bits wide
	    on the L machines, and only 8 bits wide on the N machines.
	It's true that the disk driver software on the 3670 is better than on the
	3650.  The hardware is also different, whether it's better is hard to say.
	The rest of this (the 8-bit/16-bit stuff) is not true.  The only referent
	for those numbers I can find is the bus width of the FEP microprocessor.

	Since raw disk speeds are in the 1 to 3 million bytes per second range, and
	the numbers quoted here are in the 20 to 80 thousand bytes per second range,
	I doubt that raw disk speed has anything to do with the measured performance
	of any of these file systems and network file access paths.  A few days
	with the Metering Interface (the one introduced in 7.2) would probably
	reveal some of the roots of the measured performance.  Raw disk speed does
	affect paging performance pretty noticeably, though.

	    So, 367x's make faster file servers than 3650s (if you can afford the

	I haven't tried to compare the speed of those two machines as file servers,
	but I suspect the story is much more complicated than anything that's been
	presented so far.  There are a lot of variables.  I do know that as a file
	server shared between more than a couple of people, LMFS is generally cpu
	bound.  It wouldn't surprise me if the 3675 comes out faster, but it
	might not be for the reason you think.

    3650's are better than 367x's as file servers for several reasons:

    1.  You can put more memory in.  Our experience is that file servers
    need loads of memory for LMFS buffers.

    2.  You can use 20MHz SMD disks.  3675's get best performance from 10MHz
    disks (M2294, etc.).  They can handle 15MHz disks (EMD515, etc.) but
    actually run slower with them because of frequent overrun errors.  They
    can't handle 20MHz disks at all.

    3.  You can use 20MHz ESDI disks (although you can't mix them with SMD
    disks).  This lets you have 768MB in a 5-1/4 inch disk.
The 760MB drives have a transfer rate of 15MHz and are the fastest ESDI drives
available at this time. A spec for 24MHz ESDI has been created, but there are as
yet no drives availble with this transfer. 

    4.  The 3650 disk driver has some read-ahead optimizations which help
    LMFS.  There are some things that the 3670 driver is better for, but
    LMFS is not one of them.

	I want an XL400 file server.

    So do I.