[ltp] T21, what ide speed?

[Tino Keitel]

On Tuesday, 16. October 2001 00:58, Dr. Edmund Weitz wrote:
> Sorry, I know this comes a bit late but I stored this message for
> future reference and was on vacation in the meantime.
>
> From the kernel boot messages I guess that the idebus=xx parameter
> does only affect the hard disk if it is in PIO mode. (Is that true?)
> On my (SuSE 7.3) installation, the hard disk (IBM-DJSA-232, also on a
> T21) is automatically switched to DMA mode.
>
> I played around with different settings and found out that PIO with
> idebus=66 seems to be slower than DMA on my machine. But I also found

Again: the idebus parameter only influences the PIO timings of the kernel IDE 
driver. It's not intended to speed up transfer rates AFAIK. BTW., I'm sure 
the IDE bus of your TP uses 33 MHz (the same clock as the PCI bus) and not 66 
MHz. Just be lucky that the kernel uses DMA automatically on your T21, I had 
to patch the kernel to get DMA working on my 765L.

> out - to my astonishment - that the output of hdaparm -tT doesn't seem
> to be a reliable means to tune your hard disk. With the _same_
> settings (DMA) I got results that varied from
>
>   Timing buffer-cache reads:   128 MB in  0.80 seconds =160.00 MB/sec
>   Timing buffered disk reads:  64 MB in  3.55 seconds = 18.03 MB/sec
>
> to
>
>   Timing buffer-cache reads:   128 MB in  1.25 seconds =102.40 MB/sec
>   Timing buffered disk reads:  64 MB in  7.82 seconds =  8.18 MB/sec
>
> Most of the time, the first value is approx. 140 while the second
> value is approx. 18, but I also had this strange 102/8 result. Let me
> add that this wasn't influenced by other processes running at the same
> time.
>
> Any comments?

Do you really know what you machine does in the background? IMHO the best 
would be if you do your hdparm tests in single user mode. But even then you 
won't get the same results at every hparm -Tt run. I also think that 18 MB/s 
are fast enough (even the RAID0 on my desktop machine isn't faster ;-).

Tino

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