IDE bus speeds: Are you sure you have yours set correctly?

guero61 · l33t Joined: 14 Oct 2002 Posts: 811 Location: Behind you

I always got tired of that kernel message about defaulting to an IDE speed of 33MHz and setting it with idebus=xx. That worked until I just noticed today, and it's a little different now.

Now, if you say idebus=66, you'll get a nasty message from this little print statement:

AlterEgo · Veteran Joined: 25 Apr 2002 Posts: 1619

Sorry to start a discussion in a documentation-forum,
but I have some doubts about this.

My boot message, and it's correct for my setup.

aardvark · Guru Joined: 30 Jun 2002 Posts: 576

Of you have a normal PCI motherboard, your bus speed should always be 33 Mhz (ide runs over PCI bus). This is something else than the numbers ATA 66/100/133. That is is the speed in Mb/s that the bus supports as in protocol. A PCI bus of 33 Mhz and 32 bit can theoratically support a data throughput of 33 * 10^6 * 4 bytes / sec = 133 MB/sec, which is enough for all ATA modes available today.
(one byte is 8 bits.)

Normal ATA 133 is therefore at the limit of what a NORMAL Pci bus can suport. Of course there is also 64 bit PCI and/or 66Mhz Pci bus, but you normally won't have those. Serial ATA is TNG and I don't know how that is done

Conclusion: the ide bus (or PCI) speed at 33 Mhz is just fine.
Look for transfer mode instead: hdparm -X??

guero61 · l33t Joined: 14 Oct 2002 Posts: 811 Location: Behind you

That's what I said in my original post -- I don't think it gains you anything, it was just an unconfigured "error" message that I always saw.

aardvark · Guru Joined: 30 Jun 2002 Posts: 576

shie · n00b Joined: 19 Jun 2002 Posts: 6

although, hdparm says:

xunil · Posted: Sun Jul 13, 2003 9:50 pm Post subject: Um, documentation anyone?

Here's what the idebus kernel command-line option actually means (taken from the kernel IDE documentation, /usr/src/linux/Documentation/ide.txt):

shie · n00b Joined: 19 Jun 2002 Posts: 6

i know what idebus is, i was more worried about the line

xunil · Posted: Mon Jul 14, 2003 5:16 pm Post subject:

Right, I was replying to the thread, not you.

However, your problem may have to do w/ your IDE configuration in the adapter's BIOS (whether that be your motherboard's BIOS or the BIOS on the PCI card if its an expansion adapter). Most modern IDE adapters' BIOSes allow the user to configure which "speeds" the channel can use. Your BIOS may have it configured to do PIO modes only. OTOH, if you're getting 190 for hdparm -T and 40 for hdparm -t, that's actually quite good for a single IDE hard drive. In fact, *no* consumer-grade hard drive (IDE or SCSI) can actually do more than 50-60 for hdparm -t. The ATA66/100/133 stuff is meant for doing RAID, not boosting the performance of individual drives.

taskara · Posted: Sat Aug 02, 2003 12:18 am Post subject:

so assuming I have a mainboard with 66 mhz pci bus (like dual amd machines) and that the ide controller is supported by the linux kernel, I make sure idebus=66 and I should have a peak theoretical bandwidth of 266 MB/sec for my HDDs.

Impossible to achieve sure, but what if I had a 66 mhz 3Ware serial ata hardware raid controller configured with 4X WD Raptop drives in raid 0, I may be able to surpase 133mb/sec ? :twisted:

hmmm I doubt they will be that fast, but still that's a good experiment I reakon..
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Marctraider · Guru Joined: 24 Dec 2003 Posts: 387

How can it be that on my Satellite Pro 480CDT idebus=66 DOES work?
And, it affects the HDparm results.
For the buffers only though...

It's a 4GB hd running at Pio mode 4,
The speed is 6mb/s sais hdparm, and for the other onces is was first 33mb/s
now it's 60 - 66mb/s (thanks to idebus=66)

Anyways my laptop died, could this happened because of the idebus=66?

(Edit, it didnt work at all, i just configured my bios wrong or something, i believe this option even killed my laptop)

xunil · Posted: Mon Apr 12, 2004 4:44 am Post subject:

taskara · Posted: Mon Apr 12, 2004 5:22 am Post subject:

we are talking bus speed aren't we? not transfer modes.

I dunno.. too tired..
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xunil · Posted: Mon Apr 12, 2004 6:38 am Post subject:

idebus was added for IDE drivers that could not automatically detect the PCI or VLB bus speed, such as the generic IDE driver which often cannot, and some dumb drivers that don't try to detect the bus speed and just assume it to be one value if not otherwise specified. PIO transfer modes won't work w/o the proper bus speed, so idebus doesn't make your IDE devices any faster -- it just makes them work.

Marctraider · Guru Joined: 24 Dec 2003 Posts: 387