Re: Two hdds on one channel - why so slow?

Andre Hedrick
2002-01-01T23:35:11Z

Brian,

Well if hell freezes over and I die, the patches to make the driver
handled clean low_level IO threading will never be accepted. Because they
model the state-diagrams of the physical layer of the hardware exactly in
the transport layer, it is totally orthoginal to the darwinism of Linux.
Design is a problem, it is not permitted in a darwin-evolution model.

It only allows you to access both drives on a channel and only suffer a
10% IO loss max on each, but you gain a smooth IO access to both drives.

Regards,

Andre Hedrick
CEO/President, LAD Storage Consulting Group
Linux ATA Development
Linux Disk Certification Project

On Tue, 1 Jan 2002, Brian wrote:

> This is an inherent quirk (SCSI folks would say brain damage) in IDE.
>
> Only one drive on an IDE chain may be accessed at once and only one
> request may go to that drive at a time. Therefore, the maximum you could
> hope for in that test is half speed on each. Throw in the overhead of
> continuously hopping between them and 12MB is no surprise.
>
> That is why even cheapo Compaqs and Gateways have the hard drive and
> CD-ROM on separate chains. It's also why IDE RAID cards have a separate
> connector for each drive.
>
> -- Brian
>
> On Tuesday 01 January 2002 05:34 pm, Krzysztof Oledzki wrote:
> > Hello,
> >
> > There is something wrong with ide data throughput with at last both via
> > kt133 and promise pcd20265 controllers.
> >
> > I have Asus A7V-133 Mobo with VIA KT133A chipset and onboard Promise
> > pcd20265 ide controller. My CPU is Athlon 1400 MHz and I have 512 MB of
> > PC133 SDRAM. I noticed that connecting two ata100 hdds into the same
> > channel makes everything much slower. So I made some test:
> -
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