[K12OSN] Knowledge turned crisis

Les Mikesell les at futuresource.com
Thu Dec 2 22:49:12 UTC 2004

> From: David H. Barr

> If you're going to stick with EIDE, you don't necessarily 
> need more than one card;  Typically for low-end setups I set 
> one hdd as master0, and a dvd/cdrw as slave0.  Then 3 drives 
> go in, one as master1, master2, master3 -- and voila!  
> Cheapest raid5 w/hotspare I know how to get ahold of.  
> Essentially you want to make sure they have their own 
> CHANNEL, not necessarily their own controller.

I haven't measured this but I'd expect it to cut write performance
in half if you mirror 2 IDE drives on the same controller.  Unlike
SCSI, the IDE controllers can only handle one outstanding command
at a time so writes to two drives on the same cable won't run
in parallel.  Software raid5 slows you even more because the CPU
gets involved and you force all the drive heads to seek at once
instead of independently.

> As long as one is doing software raid, though, what's the 
> problem with SATA drives?  A generic controller is less than 
> $30, and you can get 80GB models for dirt cheap.

SATA forces you to use only one drive per controller although you
can get cards with more than 2 controllers.

   Les Mikesell
     les at futuresource.com

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