Problem with recovery partition data

Alain Knaff alain at knaff.lu
Tue Apr 13 22:51:14 CEST 2004


begin  Tuesday 13 April 2004 22:17, Donald Teed quote:
> I read someone saying they had excellent performance with lzop, so
> I switched to an initrd with lzop as the default at the same
> time I picked up your latest updates on Monday.  So I guess
> it can't be data corruption on that level.  I did another test
> this afternoon - checked that the original did work with F11,
> sent it, restored to the same machine and hard drive and F11
> did not work.  This run was with the acpid stopped and KDE
> sound server not starting on the server machine.
>
> Given that a dd style of imaging should be working, where do you
> suggest I start looking for something that could be more robust?

The first thing I'd check is to do a compare (using the cmp command)
between an original (working) hard disk, and a udpcasted disk.

In order to do this, build the two disks into a same machine one on
the primary controller, one on the secondary, boot from a Knoppix CD,
(or from an udpcast CD...) and run a compare:

 cmp -l /dev/hda /dev/hdc

This not only shows whether the disks are equal, but also where
exactly the differences lie, if there are any.

It is important that between the udpcast and the compare operation, no
boot was attempted from these disks (as it might have changed some
bytes). Indeed, in Windows, even trivial activity such as moving some
window changes the registry, which is enough to make the disk image
different ;-)

You may verify, after the compare, whether F11 is broken on the
udpcasted disk.

Maybe what's going on here is that the disk's serial number (can be
displayed using hdparm -i /dev/hda) is stored somewhere in the
partition table, maybe in some scrambled form. The F11 functionality
would only works if the physical serial number, and the one in the
partition table agree?

It might be interesting to check what happens if you play back an
image to the disk where it originally came from:

Disk A ===> Disk B ===> Disk A

If that works, then I think it might be a serial number issue. (Maybe
overwrite Disk A with sth else between the two transfers, or manually
switch off the F11 functionality)

Another theory is that somehow the disk geometry as it appears to
Linux is not the complete disk, and that one or more sectors near the
end of the disk do not get copied, because for some reason the kernel
(i.e. operating system binary) is mistaken about the exact size of the
disk? If those sectors contain information that is critical for the
F11 functionality, this might explain stuff.

It's rather obvious that this is unrelated to UDP level corruption, or
else lzop would have complained very loudly.

It must be something that goes on locally in the machine.

Maybe also the manufacturer of the machine might have some info how
the F11 functionality works, unless he considers that a trade secret,
of course ;-)

Regards,

Alain



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