Date: Mon, 03 Feb 1997 10:30:12 +0200 From: Nadav Eiron <nadav@barcode.co.il> To: Andrew <andrew@ugh.net.au> Cc: freebsd-questions@freebsd.org Subject: Re: Two IDE controllers better than one? Message-ID: <32F5A214.2792@barcode.co.il> References: <Pine.BSF.3.95.970203133150.22613B-100000@mopsy.hobart.tased.edu.au>
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Andrew wrote: > > Hi, > > <background> > > I have an IDE controller built in to my IO card. It is one of these > starnge arrangments where the mother board is in two bits - one has the > processor, RAM etc and the other has all the IO stuff built in (video, > sio, lpt, FDD, HDD etc). The board origianlly came with a 386-SX-16 so you > get the idea about the sort of age (its an IPEX if thats any help). I now > have a 486DX-25 board to add to the IO part. > > I also have a ISA multi-IO card (new last year but cheap) with a HD > controller. Part of my HD is unusable due to bad blocks and so to get > enough space for FBSD I need two drives. > > <end of background> > > The question is - is it better (ie faster, take less RAM, whatever) to > connect each drive to a seperate controller or (perhaps because of the age > of the builtin contorller, is it better to stick them both on the multi IO > card which appears to allow two drives to be connected (the motherboard > controller only allows one)? > > Should I just try both and run a benchmark and see what I come up with? > > Thanks, > > Andrew <(E)IDE Background> IDE controllers *always* (AFAIK) control two drives per channel. Each channel has a single 40 pin connector and you can daisy-chain two drives on such a connector, simply by using a flat cable with three connectors on it. Most modern chip sets support two such chennels, for a total maximum of four drives. The two channels are usually called "primary" and "secondary" channel, while the devices on a single channel are called "master" and "slave". The master and slave on a single channel cannot be accessed concurrently. However, the primary and secondary channel are completly separate, and assuming you don't have a buggy chip set (called the CMD640) *can and will* be accessed concurrently. Newer controllers and drives have EIDE features. There are basicaly two of those: 32 bit transfers (you can't get that from an ISA card though), and PIO modes 3 and 4. If your BIOS and drives supports those you can get better performance. Your old controller probably does not have those. I doubt that your drives, or even the new controller (if it`s ISA) supports it either. <End of (E)IDE background> So: If you have two separate channels you'll probably gain performance by distributing the load between them. If you have an IDE controller with one 40 pin header it can probably control two drives on that. If you want real performance get SCSI. Hope this helps, Nadav
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