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Conference giadev::decstation

Title:DECstation PC Conference
Notice:register note 2, see notes 3 & 4
Moderator:TARKIN::LININD
Created:Tue Jan 10 1989
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:7470
Total number of notes:34994

7340.0. "Eide DMA vs SCSI" by CGOOA::SMCLEAN () Wed Feb 05 1997 16:37

    
    In response to a tender document, the following question has been
    posed. Can anyone provide assistance?
    
    
    "Is true DMA transfer supported for E-IDE drives running under NT 4.0
    on the (current) Celebris GL systems?"
     
    Or would they be better off installing SCSI drives?  What kind of
    performance increase would they expect by installing SCSI drives (wide
    or Narrow)?
    
    Unfortunately, they did not provide any info on the applications this
    system would running.
    
    Thanks steve
    DTN 638-6941
T.RTitleUserPersonal
Name		DateLines
7340.1PCBUOA::KRATZWed Feb 05 1997 17:0920
    Well, this is somewhat involved...
    The PCBU was FIS'ing an IDE DMA driver on NT 4.0 until we switched
    from Toshiba CD-ROMs to Goldstars, whereupon CD audio broke, so we
    went back to using ATAPI.  You can check by firing up the Services
    icon in Control Panel and looking for PIIXIDE.  If it's there (and
    ATAPI is disabled), you're doing DMA.  If ATAPI is enabled, you're
    not.
    
    The Seagate Barracuda (7200rpm) benchmarks faster than the Quantum
    EIDEs (even with DMA).  However, to save some (serious) bucks, the
    Barracuda was replaced with the Quantum Fireball Tempest SCSI, which
    is no faster than EIDE (in fact, now slightly slower than the equivalent
    2.1Gb EIDE model; same disk, now there's SCSI overhead).  If things
    are normal (i.e. FUBAR...), you can't tell which SCSI disk you'll get
    from the SKU order number (only the BOM) until the Barracuda's are
    completely used up.
    
    Keep in mind typical benchmarks don't tend to take advantage of
    DMA... the processor is just sitting there waiting anyhow.
    .02 K
7340.2Don't limit the scope to one issue.SNOFS1::RASMUSSENThu Feb 06 1997 18:4417
Do we not need to be very careful here? If we look at individual device
performance the issue of SCSI verse EIDE may lean to EIDE based on cost
performance. However, it is my understanding that SCSI will become more
attractive when you consider:

1)	Limitation (verses SCSI) of total number of EIDE devices
2)	Impact of concurrent I/O i.e. SCSI much better in this area.
3)	Variety of SCSI supported devices (eg. scanners) - no need for
	new interface cards (assuming <= 7 SCSI devices total).
4)	SCSI support for external devices (eg. Tapes, CD-ROM writers)

So besides individual disk performance you do need to consider overall
system performance and possible upgrades. 

Wayne
7340.3eide vs scsiCGOOA::SMCLEANThu Feb 06 1997 19:036
    Guys,
    
    	Thanks for the comments.  I will discuss the options with the
    customer and the account manager.
    
    Thanks steve....