[Gllug] SCSI more reliable than Maxline PlusII?

[Bryn Reeves]

On 08:49 Fri 10 Sep     , Chris Bell wrote:
> On Fri 10 Sep, Garry Heaton wrote:
> > 
> > Disregarding read/write speed and given a decent hardware RAID card, are
> > SCSI disks mechanically more reliable than the best SATA disks? An assistant
> > at GND (www.gnd.com) suggested Maxtor's Maxline PlusII disks are
> > mechanically a fair match for SCSI.
> > 
> > Garry
> > 
>    I heard that a disadvantage of IDE was that master and slave received the
> same address commands. This could cause multiple discs to search for every
> address, causing excessive mechanical wear. Other suggestions were that SCSI

This doesn't sound right to me. IDE is certainly a far simpler spec than 
SCSI (limited to two devices per bus, limited class of devices, etc), but
I'm pretty sure that addressing commands are *not* executed by both master
and slave on a bus. Think about it. If the two devices are radically
different in size/geometery, the address values for one may not even be
valid on the other, causing seek errors etc. My understanding has always
been that the master/slave were wholy independently addressable. 

> discs have better bearings, are assembled with greater care, and subjected
> to more extensive testing. They may use semicondutors and other components
> designed and manufactured to a higher "military" spec, for use under extreme
> conditions. Some drives are guaranteed for very long life, but is a better
> guarantee paid for by the increased price? I suspect that we may treat
> explanations in the same manner as we treat government spin.

This is more like it. My understanding was that there are three main 
reasons for the price difference:

1) markets. 
  IDE is mass-market, high volume technology. Look at the way DRAM price
  rockets as soon as a particular type is no longer shipping large numbers
  of units.

2) testing/warantees.
  SCSI devices demand more intensive unit and design testing, and also the
  cost of backing up the m'frers warranty over the extended lifetime of 
  these devices.

3) interface hardware.
  SCSI host/device interface hardware costs *a lot* more than IDE. IDE's 
  big goal was always low-cost mass implementation. SCSI chipsets implement
  much more in hardware than IDE, like s/g, command queueing and DMA (IDE 
  normally uses the DMA controller on the motherboard chipset). 

Arstechnica has a nice little SCSI primer which goes into some more 
detailed comparisons:

http://arstechnica.com/paedia/s/scsi-1.html

Cheers,

Bryn.


> -- 
> Chris Bell
> 
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