On Sat, 12 May 2007, Brian J. Murrell wrote:
> On Sat, 2007-05-12 at 21:12 -0400, Stuart D. Gathman wrote:
> >
> > The interrupt rate has nothing to do with the type of disk, and a lot to
> > do with the controller. There is a CPU difference between $50
> > consumer IDE/SATA adapters, and $300 server grade IDE/SATA adapters.
> > You'll want the controller to support fast DMA at minimum.
>
> I thought the biggest thing that SCSI had that IDE didn't was SCSI's
> ability to shovel an ass-barn-load of data to a disk and the disk would
> go deal with it, giving up the SCSI bus so that another disk could be
> shovelled another ass-barn-load of data to go and deal with, and so on.
>
> ...
>
> The contrast with IDE (or PATA as I guess the trendy name is), again as
> I always thought was that the IDE bus was not available for use while a
> disk was still pending a media I/O operation, so that with multiple
> devices, you could not leverage the I/O of the IDE bus using multiple
> devices, essentially in parallel. I guess this is where having system
> with multiple IDE buses and only putting a single device per bus grew
> from.
We always put exactly one IDE disk per channel for that very reason.
You are correct that with 2 disks on the same channel, only one can
be active at a time. So don't do that. A $50 IDE PCI card give you 2 IDE
channels - for 2 disks in high performance mode (suitable for mirroring).
Buy two cards for 4 disks. Or a $300 server card for 8 disks.
> How does SATA fit in with all of this? Is it basically the same
> limitations on the bus as IDE/PATA, so that you'd really not want to put
> more than 1 device per bus?
SATA mandates at most 1 disk per channel, making the issue moot. It is
still true that there is only one active disk on a bus. But then there
is only one disk on a bus.
--
Stuart D. Gathman <stuart@bmsi.com>
Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.
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