[mythtv-users] The Bigger... Disk contest, Fall 2007 edition

Brian Wood beww at beww.org
Fri Oct 19 16:45:36 UTC 2007


David Brodbeck wrote:
> On Oct 18, 2007, at 12:50 PM, Jay R. Ashworth wrote:
> 
>> On Thu, Oct 18, 2007 at 12:22:47PM -0700, David Brodbeck wrote:
>>>> The SCSI drives will; I've done it.
>>> Fair enough, but I don't think valid anymore to assume SCSI = "server
>>> class" and non-SCSI = "desktop class."  The Seagate Barracudas have a
>>> 24x7 duty cycle, whether they're SAS or SATA.
>> Well, that's what we use, and we had one decide, about a year into  
>> it's
>> duty, maybe 2 tops, that if you tried to read a certain range of
>> sectors, *it would make the IDE controller drop off line, until
>> powercycle*.
> 
> Well, if you want to talk about the electrical robustness of the  
> interface, I agree IDE is not very good.  Neither is SCSI, though --  
> one bad device can bring down all of them on the daisy chain, which  
> in the case of SCSI can been up to 15 devices instead of just  
> two. ;)  I think SATA's "one drive per port" concept is a good one.
> 
> I kind of soured on SCSI after a while because it was so difficult to  
> get all the devices to agree on proper termination.  Eventually you  
> get tired of fiddling with (and losing) the little resistor packs.   
> And you can get yourself in trouble in strange ways with external  
> SCSI, even do damage to devices with it.  I once had a tape robot  
> that kept failing under warranty.  After a few months it would stop  
> talking to the computer and have to be sent in for repairs.  After a  
> couple of rounds of this, the tech support folks happened to ask how  
> long a cable I was using.  We determined it was too long and I  
> swapped it for a shorter one.  The tape drive still didn't work and I  
> exchanged it, but I kept the shorter cable in place, and it never  
> failed again.  Ironically, the too-long cable was the one that had  
> shipped with the drive.

I discovered that virtually all of my SCSI termination problems went
away when I went to active termination, as opposed to passive resistors.

Using good quality cables also makes a difference, as does staying away
from devices that use DB-25s for SCSI. You want a cable that has a
separate ground conductor for each data line, not one common one for all
of them.

Using the same type of cable for each link in an external chain is also
a good idea, nor some hodgepodge from your junk drawer.

Going to low-voltage differential units, instead of the earlier
single-ended ones, also helps, especially at high speeds or with long
cables.

Like anything else SCSI works well if you do it correctly and don't try
and cheap out, but ATA type interfaces are certainly in more common use
for home systems. PCs are marketed based on CPU speed because most
buyers of such machines do not know or even care that the rest of the
machine can't come close to keeping up with the CPU, while commercial
servers are usually rated based on benchmark suites that test all
aspects of the hardware.

beww


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