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On Mon, 9 Oct 2000, Andre Tomt wrote:

> Using a newer ATA66 IBM 7200rpm drive, on a VIA chipset, I can sustain
> 24-25mB/s in both UDMA33 and ATA66 mode. This is a Athlon Asus

This okay, the drive has a physical data IO limit for sustained, not
burst. Thus getting 24-25mB/s in both UDMA33/ATA66 falls under the
limits of each standard.

Now the drives that I have that are 37-42mB/s would exceed the UDMA33.
You have to understand that in order to get data out you must issue the
seek instruct (build and send) then read/write data.

Much of the overhead in drive IO is getting there or building the command
to do the data part of the IO.

> using hdparm -X68 -d 1 -c 1 -k 1 -K 1. That's even with the linux-ide.org

If you start muckying with the drive setup after you selected the kernel
auto-tune or active programming you could have problems.

Not all chipset code reprograms the host when changing the drive rates.
Thus you can/will cause an IO sync error.

> I was talking 24-25mB/s - not 100mB/s. Biiiig difference ;-)
>
> The 10k rpm u160scsi drive, yet again a IBM, sustains
> about 34-38mB/s.
>
> Remember, I'm not talking fragmented reads here. Thats is a whole
> different universe. .

Recall that I told you that there is a physical limit of getting stuff off
the drives. The platter density is to low and the rpm's are to slow to
get there yet. Remember it took second genration ATA66 drives to fill
the ATA33 bandwidth.

Cheers,

Andre Hedrick
The Linux ATA/IDE guy

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