Re: error: no such disk

[Nick Martin]

2009/12/28 Michael Evans <address@hidden>:
> On Sat, Dec 26, 2009 at 1:40 PM, Leslie Rhorer <address@hidden> wrote:
>>> The issue I'm still having, and still had when the suggested changes
>>> were made, is that grub says there is no such disk; I'm then presented
>>> with the grub rescue prompt and I'm unable to ls any of hard drives. I
>>> can, however, do an ls and see all the hard drives themselves, I just
>>> can't ls their contents. When I do an ls of any of the partitions I
>>> get an unknown file system error.
>>>
>>> Could the insmod ext2 line be the cause? (hd1,4) is an ext4 partition,
>>> but the ext2 module is being loaded. I checked to see if I have an
>>> ext4 module: I don't. But this shouldn't matter because ext4 is
>>> backwards compatible with ext2.
>>
>>        Well, there's "backwards-compatible", and there's "backwards
>> compatible".  I am not familiar with ext4, but it is entirely possible the
>> ext4 module can read ext2 partitions, but an ext2 module cannot read ext4
>> file systems.  If the failure you are getting happens after the Linux kernel
>> and initrd are loaded, then this sounds like an issue in the initrd image.
>> If this is the case, you might try updating the initrd image via whatever
>> method your distro employs.  If the failure is happening in the grub loader
>> before the Linux kernel is loaded, then it is an issue with grub.
>>
>>> The issue I'm still having, and still had when the suggested changes
>>> were made, is that grub says there is no such disk; I'm then presented
>>> with the grub rescue prompt and I'm unable to ls any of hard drives. I
>>> can, however, do an ls and see all the hard drives themselves, I just
>>> can't ls their contents. When I do an ls of any of the partitions I
>>> get an unknown file system error.
>>
>>        Um, OK.  That's a little convoluted, but I think I see what you are
>> saying.  If grub cannot read the file systems (ext4 or whatever), then it
>> can never see the structures allowing it to find the stage 1 loaders or the
>> Linux kernel, which may reside in /boot/grub, /grub, /boot, /, or whatever.
>> In my particular case, I have tiny ext2 partitions containing only the Linux
>> kernel and initrd files in / and the grub files in /grub.  Grub sees these
>> as simply / and /grub on /dev/md1 ( hd0,0 or hd1,0, as the case may be ).
>> Once the kernel is loaded and the md module is active, /dev/md2 (consisting
>> of hd0,1 and hd1,1) is mounted on / and then /dev/md1 is loaded on /boot.
>> The point is, grub must be able to recognize the file system where the
>> kernel and the grub files are found.  If the grub menu (menu.lst) comes us,
>> then grub is finding menu.lst, and it recognizes the boot partition at least
>> well enough to try to pass over control to the kernel.  If not, then in
>> order to fix the problem, you are going to have to provide grub with a file
>> system it does recognize.  Whether that file system can be ext4 or not, I
>> don't know.  That's one reason why I have a separate boot partition.  It
>> allows the boot file system to be as rudimentary and / or widely supported
>> as possible, while allowing the other file systems to be as new or have as
>> many bells and whistles as I want.
>>
>>
>>
>> _______________________________________________
>> Help-grub mailing list
>> address@hidden
>> http://lists.gnu.org/mailman/listinfo/help-grub
>>
>
> I agree, ext4 is backward compatible to a point.  There are features
> which are important to ext4 performance and benefits which break the
> backward compatibility.  Ideally you use ext2 or at best ext3 for your
> boot file-system (the difference being only the journal), and have all
> the files you want to load on it.  I am not familiar with grub2's
> development, and don't know anything about filesystem support
> currently in planning or development; you should look at the wiki
> and/or website for documentation; though I would take the path of
> least resistance and follow the currently working feature-sets.
>

I did decide to take the path of least resistance. My /boot partition
was ext2; I feel it should have worked, but I didn't want to spend
forever figuring out what was wrong, so I just let the Ubuntu install
use the whole of my /dev/sdb disk, deleting the large ntfs partition.
Everything works now and I still don't know what was wrong before.

Thanks for your help guys.