Re: Large hard disk support in FreeBSD

From: Robert Watson (rwatson_at_FreeBSD.ORG)
Date: 07/29/03

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    Date: Mon, 28 Jul 2003 20:10:39 -0400 (EDT)
To: Chris Howells <lists@chrishowells.co.uk>

    On Mon, 28 Jul 2003, Chris Howells wrote:

    > I'd like to put a 60GB hard disk into Gateway 2000 Pentium 150 (from '96
    > or '97 or so I think) running FreeBSD 4.8 RELEASE.
    >
    > Can anybody tell me how successful this is likely to be? Will I be able
    > to use the full capacity of the drive?
    >
    > I seem to recall that the trick with large hard disks and old BIOSes is
    > to disable the drive in the BIOS and let the OS detect the disk
    > itself... is this the case with FreeBSD as well?

    Up until relatively recently, my main personal web service box was a
    Gateway 2000 P120 from '95 running FreeBSD 4.x, so I can speak to this
    with some confidence :-). There are a few things you need to look at:

    (1) BIOS revision. Make sure you've flashed your BIOS forward as far as
        possible -- some older Gateway 2000 BIOS's will hang if they see a
        driver larger than they think is possible (I'm sure there's a better
        technical definition, but the result is clear regardless :-).

    (2) Do you want to boot from the drive? If I might suggest--don't even
        try. Boot from a drive known to work fine with the BIOS. As you
        suggest above, leave the drive unprobed (disabled) in the CMOS
        configuration, which will help prevent the BIOS from tripping over it.
        this will mean you can't use the drive in the loader before the kernel
        is loaded, but since FreeBSD's device probing and management is pretty
        much independent of the BIOS, it should work fine with FreeBSD.

    (3) The ATA controller built into your motherboard may not support larger
        disk addressing, although I think that shouldn't be a problem with
        60GB. If you try to use a drive larger than addressable using the ATA
        controller, you may want to pick up a cheap PCI ATA controller (or get
        the "kit" version of the drive that has a new controller).

    (4) Cabling and support for non-PIO. I found that my older motherboard's
        ATA controller had problems negotiating higher rate transfers from the
        disk, so ended up disabling the DMA support for at least one of the
        drives I added. You will probably also want to make sure you're using
        the newer cable that will come with any recent drive, since that will
        help avoid quality and negotiation problems. You might end up needing
        to force PIO support anyway if you're getting occasional timeouts from
        the drive.

    That said, I ran just fine for about 8 years on my p120 -- I didn't want
    to take it out of service, but I needed more memory than the chipset could
    comfortably support. Some of those systems can only cache the first 64MB
    of memory, so any additional memory is used uncached. I ended up
    upgrading it to an E-Machine, go figure :-). The old p120 is now back at
    home from colocation, and I'm sure I'll find a use for it at some point.

    Robert N M Watson FreeBSD Core Team, TrustedBSD Projects
    robert@fledge.watson.org Network Associates Laboratories

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