(E)IDE and ATA were designed and manufactured in order to connect two disks
to one channel, using one cable. Generally this was regarded as a
non-desirable configuration, as the standard does not allow for the two
disks to be addressed simultaneously.
Usually one controller has two channels. I think attaching the two disks to
separate channels of the same controller does allow for paralellism.
The situation for sata is practically identical, but they skipped the
two-drives-on-one-channel bit that was a bad option anyhow. And they made
the cabling more flexible :)
So if you want to have many disks, you need to have many controllers.
SCSI of course still is an option. With SCSI you can drive multiple devices
simultaneously in the same channel (yeah I know it's called a bus), its just
that you are sharing bandwith.
Cheers,
Bart
On 8/17/06, Chuck Norcutt <chucknorcutt@xxxxxxxxxxx> wrote:
>
> I haven't been into the nitty gritty of PC disk controllers for about 15
> years but it used to be that dual channel IDE/EIDE controllers (at least
> those on the motherboard) did not offer any parallelism. I don't know
> if that situation has changed over the years or is any different with
> SATA. I suppose there is some degree of overlap with each drive being
> able to work out of a cache for awhile but even an 8MB cache isn't very
> large relative to the amount of data being moved these days.
>
> So, how does one achieve true drive parallelism these days without
> resorting to SCSI?
>
> Chuck Norcutt
>
> Bart Wientjes wrote:
> > Oops. I didn't. I lied. Sorry. :o)
> >
> > The raptors are each on a separate channel (Duh! sata: of course they
> are),
> > but as my mainboard only features one controller, they are on the same
> > controller. However, some of the newer mbs have two controllers,
> allowing to
> > connect each disk to its own. Now I come to think about it, I'm not sure
> > there is an advantage in using two controllers over one.
>
>
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