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

Brian,

This was true in the past and with many older drivers. However when and
if the new driver I have is adpoted, it will make SCSI cry. So please
stop polluting the issue.

Let me be as objective as I can be.

I built a special Mylex 3-channel raid 10 systems using 6 15K drive at
Ultra160. Given that I was clever, I was able to push that system to read
and write at 170MB/sec. I was very impressed by this performance, however
this was hardware raid, caching of 256MB, and 66/64 pci bus. This was a
dual PIII w/ 2GB of EEC-Buffered-Registered.

Now I have managed to use two hosts w/ 4 channels no caching controller,
no hardware raid, 4 7200RPM drives and software raid 0. I was able to
push 109MB/sec writing and 167MB/sec reading.

Also under a similar environment, I was able to, using a single card, 4
drives, not hardware-raid, no caching controller, reach 90MB/sec writing
and reading was about 78MB/sec.

Now lets adjust cost of componets and SCSI loses big.
Once there are 10K ATA drives in the market, and none exist that I know of
to date even in beta, then we can retest .

In the meantime here is another dose of reality.

http://www.tecchannel.de/hardware/817/index.html

Regards,

Andre Hedrick
Linux ATA Development

On Wed, 2 Jan 2002, Krzysztof Oledzki wrote:

>
>
> 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.
>
> So?!? This ATA100 and ATA133 standards do not make any sens? It is not
> possible to have more than 66 MB/sec with on drive and is seems that it is
> not possible to use more than ~30MB/sek of 100 or 133 MB/sec ATA100/133
> bus speed with two HDDs. Oh :(((
>
> Another question - why ATA100/ATA66 HDDs are so slow with UDMA33?
> With new IBM 60 GB IC35L060AVER07-0 I have much more than 33 MB/sec with
> ATA100 and only 24 MB/sec with UDMA33 (Asus P2B with IntelBX). New 80GB Seagates
> (Baracuda IV) have the same problem.
>
> Best regards,
>
> Krzysztof Oledzki
>
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