Date: Fri, 30 Apr 1999 20:26:24 +0100 (BST) From: Doug Rabson <dfr@nlsystems.com> To: Ken Harrenstien <klh@us.oracle.com> Cc: freebsd-fs@freebsd.org Subject: Re: When is a FFS not a FFS? Message-ID: <Pine.BSF.4.05.9904302024040.59263-100000@herring.nlsystems.com> In-Reply-To: <CMM.0.90.4.925488873.klh@churchy20.us.oracle.com>
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On Fri, 30 Apr 1999, Ken Harrenstien wrote:
> I'm a relative newcomer to FreeBSD/NetBSD and have run into some
> problems with the filesystem code that have me both puzzled and
> concerned. Hopefully this is the appropriate list and someone can
> quickly set me straight.
>
> I have a number of large disks with UFS filesystems and data generated
> by non-BSD systems such as Alpha Digital Unix and SPARC Solaris. So
> far I've been able to directly mount and use Alpha D/U drives under
> both NetBSD/i386 and NetBSD/Alpha, and this has been a TREMENDOUSLY
> useful capability. (I've also noticed with admiration that the NetBSD
> filesystem code includes provision for detecting and handling byte
> swapping, which I'm hoping will permit me to eventually use SPARC
> drives as well.)
>
> However, to my surprise this doesn't work for FreeBSD/i386 (at least
> the 3.1-RELEASE version I have), and I'm not sure why. The magic
> numbers are the same and the structures look the same, but any attempts
> to mount simply fail:
>
> # mount /dev/da5a /mnt
> mount: /dev/da5a on /mnt: incorrect super block
>
> Trying to examine the disklabel typically gives:
>
> # disklabel da5
> disklabel: ioctl DIOCGDINFO: Invalid argument
>
> But if I instead use "disklabel -r da5" it *does* read and print the
> correct disklabel information.
>
> My current theory (wild guess) is that for some reason the disklabel
> information from the disk is never taking up residence in the system
> proper, which means any reference to the [a-h] partitions will return
> bogus data. And that reason probably has something to do with
> interference by whatever code handles the DOS partition ("slice") table
> from the boot sector; possibly an unfortunate artifact of PC-centricism.
>
> Or is FreeBSD FFS really different from NetBSD FFS? D/U UFS? Why is
> there a ufs/ffs/* and ufs/ufs/* if according to the doc they're the same?
> I'm lost.
>
> I have enough disk backup that I'm willing to help alpha-test any fixes
> that might be forthcoming. I do hope I'm not the only one who thinks
> filesystem compatibility is an incredibly handy and useful feature...
FreeBSD/alpha will mount UFS filesystems from NetBSD/alpha and OSF1 with
no problems at all. Your problem is that FreeBSD/i386 puts the disklabel
at a different place on the disk from the alpha OSs. On the alpha, the
disklabel is stored at offset 64 in block zero but on FreeBSD/i386, it is
stored at offset zero in block one of the FreeBSD fdisk slice (which can
be anywhere).
I don't think FreeBSD/i386 is going to be sharing disks with different
disklabel policies any day soon.
--
Doug Rabson Mail: dfr@nlsystems.com
Nonlinear Systems Ltd. Phone: +44 181 442 9037
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