[mythtv] performance

Harondel J. Sibble mythtv-dev@snowman.net
Sat, 14 Dec 2002 10:52:28 -0800

On 14 Dec 2002 at 10:24, Henk Poley wrote:
> I'm not sure if this isn't some difference in the IDE vs. SCSI protocol,
Actually IDE is a dumbed down version of the scsi spec.  Not this statement 
doesn't apply the serial ata and serial scsi specs which oddly enough will 
allow one to use serial ata drives directly connected to the serial scsi bus. 
Not sure how they are pulling that one off.

> but SCSI drives are most of the times quite faster (and have lower
> responstimes). 
That depends, just like you have ata33, ata66, ata100 etc, there are also 
speed scales in scsi: narrow (5 or 10mb/s), wide (20mb/s), ultrawide 
(40mb/s), ultra2 (80mb/s), ultra3 aka Ultra160 (160mb/s) and Ultra 320 and I 
think I just heard about Ultra 640 which is supposed to compete with Serial 
Attached SCSI.  In many cases the drive mechanism is identical to the ide 
drive, they just have different interface boards.  OTOH, there are some 
drives that only exist in the scsi space and offer some serious raw 
performance, however they are loud!!!, hot and VERY expensive.

Also you have to realize that the speeds above are not representative of the 
drives themselve, but of the bus saturation. IOW, to really get U160 speeds, 
you'd need multiple drives all using the scsi bus concurrently.  This is one 
of the great advantages of scsi in that the controller can talk to multiple 
drives concurrently and the drives are smart enough that the controller can 
give them a bunch of tasks and say, don't bother me again until you've 
completed them all.

> They are also 1/4 to 1/2 the size for a disk you still can afford. 
That's reasonably accurate although you can find some good deals on ebay. I 
bought my Fujitsu 36gb Ultra2 drive for about us$100 a year ago that way.  
The same drive here sold for about US$250.

Harondel J. Sibble 
Sibble Computer Consulting
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