Re: [gentoo-user] ext3 partition dissapeared :(

[Alan McKinnon]

On Wednesday 24 January 2007 20:37, jcd wrote:

[snip]

> "Everything was fine" mean; I created partition and then formatted it
> without any errors or warnings. There are messages from syslog:
> ---------------------------------------------------------------------
>-- Jan 22 23:43:16 localhost EXT3 FS on sdb1, internal journal
> Jan 22 23:43:16 localhost EXT3-fs: mounted filesystem with ordered
> data mode.
> ---------------------------------------------------------------------
>-- Then I copied my data to this new partition. I could access this
> data from new partition without any problems. Next day:

OK, so we will assume that the data was written correctly

> ---------------------------------------------------------------------
>-- Jan 23 10:23:46 localhost VFS: Can't find ext3 filesystem on dev
> sdb1.
> ---------------------------------------------------------------------
>--
>
> > It looks like when you moved the data onto the new partition, it
> > got written somewhere on the disk. However, the kernel's idea of
> > how the partitions are laid out at that time and what fdisk just
> > wrote to the disk probably don't agree and the kernel had got it
> > wrong.... This does happen when you delete two or more partitions
> > and create one large one.
>
> Why it can happen when replacing two partitions with large one?

First thing to know, is that the PC has the most insane internal design 
of any electronic device ever made anywhere in the world at any time, 
ever. (Well, Thomson aircraft radios are actually worse, but you get 
the idea...). The result is that not everything makes sense... When the 
kernel boots, it reads the partition table off disk and knows that the 
first partition starts at cylinder 0 and the second partition starts at 
say cylinder 2000. The kernel doesn't update this information when you 
run fdisk, so if you delete two partitions and create one big one, the 
kernel can get confused. It's not hard to fix on the PC, but Linux runs 
on 20 architectures that are not all as crazy as Intel PCs, which might 
be why this oddity is still there are 15 years. Redhat have a utility 
called partprobe that gets everything back in sync after using fdisk, 
but I have yet to find it in Portage

> I tried gpart with this output:
> ---------------------------------------------------------------------
>-- #gpart /dev/sdb
> Begin scan...
> Possible partition(Windows NT/W2K FS), size(40959mb), offset(0mb)
> Possible partition(Linux ext2), size(197512mb), offset(40959mb)
> End scan.

[snip]

According to this you have an ext2/3 partition as the SECOND partition, 
not the first, and it does not cover the whole disk.

Are you absolutely sure you pressed "w" in fdisk after creating the 
partitions? It sure looks to me like your changes were not written to 
disk. Try mounting /dev/sdb2

alan
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