[ltp] T21, what ide speed?

[Dr. Edmund Weitz]

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
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?

Thanks,
Edi.





Friedemann Baitinger <fb@baiti.net> writes:

> I am just wondering at what speeds you operate your IDE busses in the
> T21. By default even linux-2.4.9 selects idebus=33. I have experimented
> with appending "idebus=66" to the kernel commandline and so far it seems
> to work with that speed too. I have not done any elaborate performance
> comparisions. At idebus=66 setting I get:
> 
>   [root@blackbox baiti]# hdparm -tT /dev/hda
> 
> /dev/hda:
>  Timing buffer-cache reads:   128 MB in  0.99 seconds =129.29 MB/sec
>  Timing buffered disk reads:  64 MB in  4.05 seconds = 15.80 MB/sec
> 
> 
> has anybody tried ata100 mode? Is that supported by the hardware at all?
> 
> -- 
> Friedemann Baitinger      fb@baiti.net       http://baiti.net/fb/
> 
> 
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