Re: Network file transfer rate comparisons

[Charles Hornig <Hornig%alderaan.scrc.symbolics.com@RELAY.CS.NET>]

    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
	maintainance).

    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.

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.