Re: UDMA 100 / PIIX4 question

[Tim Moore <timothymoore@bigfoot.com>]

Jeremy Jackson wrote:
> 
> Tim Moore wrote:
> > 15MB/s for hdparm is about right.
> 
> Yes, since hdparm -t measures *SUSTAINED* transfers... the actual "head rate" of data reads from
> disk surface.  Only if you read *only* data that is alread in harddrive's cache will you get a speed
> close to the UDMA mode of the drive/controller.  The cache is around 1Mbyte, so for a split-second
> re-read of some data....

Apologies for the too brief answer.  Sustained real world transfer rates for the PIIX4 under ideal
setup conditions and a quiet bus are 14-18MB/s.  Faster disk architecture and forcing ide driver
parameters will not change this.

Here's what you might expect from this disk family with an ATA-66 capable chipset:

[tim@abit tim]# hdparm -i /dev/hda; hdparm -tT /dev/hda

/dev/hda:

 Model=IBM-DTLA-307020, FwRev=TX3OA50C, SerialNo=YH0YHF45553
 Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
 RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=40
 BuffType=DualPortCache, BuffSize=1916kB, MaxMultSect=16, MultSect=off
 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=40188960
 IORDY=on/off, tPIO={min:240,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes: pio0 pio1 pio2 pio3 pio4 
 DMA modes: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 *udma4 udma5 

/dev/hda:
 Timing buffer-cache reads:   128 MB in  0.81 seconds =158.02 MB/sec
 Timing buffered disk reads:  64 MB in  1.85 seconds = 34.59 MB/sec

Larger sustained transfers are about 75% of the burst/cache influenced hdparm timings.

[tim@abit tim]# time dd if=/dev/hda of=/dev/null bs=1k count=500k
512000+0 records in
512000+0 records out
0.340u 6.780s 0:19.68 36.1%     0+0k 0+0io 115pf+0w
[tim@abit tim]# echo "512000/19.68" | bc -q
26016

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