[Gllug] IDE issues

Christian Smith csmith at micromuse.com
Mon Apr 15 17:27:40 UTC 2002

On Mon, 15 Apr 2002, Stephen Harker wrote:

>On Mon, 15 Apr 2002, Bruce Richardson wrote:
>> On 15/04/02, 11:26:30, Kim Hawtin <kim at aldigital.co.uk> wrote regarding Re: 
>> [Gllug] IDE issues:
>> > this may sound like a silly question, but have used the new fangled
>> > high density cables?
>> Aye, if you use a standart IDE cable then it falls back to slower UDMA 
>> settings.  The new cables are distinctive, being round and colour coded 
>> to show which end goes where.  
>> http://www.cablesnmor.com/images/round-ide-cables.jpg
>Yep I used the new-fangled fancy-coloured IDE cable. I tried to plug a DVD 
>drive into the second IDE channel with a regular cable and it wouldn't 
>even boot! So I had no choice on that one. I haven't fiddled with the DMA 
>modes yet in BIOS so I'll try that.

When doing the update, do you have excessively high system usage. If so, 
then this would indicate that the drive is in PIO mode, which I believe 
generates an interrupt for each byte transferred! DMA is generally not 
turned on by default.

To check, run:
# hdparm -d /dev/hd?

If it comes back with:
 using_dma    =  0 (off)

Turn it on with:
# hdparm -d1 /dev/hd?

You might also want to use 32bit transfers, and multicount sector 

# hdparm -d1 -c1 -m16 /dev/hd?

This should set multi-sector to 16, which most drives appear to support in 
my experience. Maybe even try 32.

Finally, before and after doing the above mods, try 'benchmarking' the 
drive using the -T and -t options to hdparm. In unoptimised PIO mode, 
you'll maybe get 3-8 MB/s with a modern drive. With DMA, 32bit IO and 
multi-sector transfer, that should go up to ~40 MB/s, a substantial 
improvement, and with MUCH less overhead on the CPU.

# hdparm -Tt /dev/hd?
 Timing buffer-cache reads:   128 MB in  0.49 seconds =261.22 MB/sec
 Timing buffered disk reads:  64 MB in  1.70 seconds = 37.65 MB/sec

>Ta all.


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