[ILUG] Scsi speeds?

[Declan Moriarty]

On Thursday 28 March 2002 17:57, Paul Jakma wrote:
> On Thu, 28 Mar 2002, Declan Moriarty wrote:
> > Can't See It' stage, what sort of Meg/S could I reasonably expect?
> > Clearly not anywhere near the 78.5Meg/s, but would it be worth the
> > expense?
>
> probably not..

That's clear enough and just about what I wanted to know, thanks.
>
> if it's a RedHat 7.x box: have you looked at /etc/sysconfig/harddisks?
Mandrake 8.0 actually. Basically the Same thing but better package choice, 
and a few scripts. I'll sort that file - It is tuned right back to PIO 4 :-(

> Hdb achieve 12MB/s. Ringing has been known to occur between disks when 
> thrashed.
ringing? ??

Yes, a hardware condition where seeks to one drive 'ring' on the bus and the 
second drive(say, hdb) answers to a seek on hda. Very bad news from an 
optimising point of view. High impedance lines in ribbon cables will often 
appear to switch like the ones beside them, due to capacitance. I've seen it. 

I should explain. As a Mandrake crashtester, one of the things I tested was a 
'driveopt' script which came with a database of drives, and max modes. It 
would try all the various modes of dma, select the fastest safe one, and 
record speeds for bulk transfers. The drives don't get thrashed like that in 
real life here - I have dos/win on one, and linux on the other. DMA2 lost the 
Maxtor disk altogether, so it had to stay on dma. The Fujitsu drive was only 
happy on something like UDMA2. Having both set so differently  on the same 
cable confused the Fujitsu when the maxtor was being thrashed, so some 
backing off in the interests of common sense was required. I don't get 
corruption, but the biggest reason to upgrade is disk access.

Mandrake sent their 8.0 kernels out with dma nobbled for apollo chipsets 
(Like mine), as the hardware problem with the apollo chipset was just 
breaking when they released. I was using their unmodified 'linus' kernel 
because the disk access otherwise PIO 4 :-/. 
-- 
	Regards,


	Declan Moriarty




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