[Nottingham] Partition problem

[Duncan John Fyfe]

On Sat, 1 May 2004, Martin wrote:

> All good stuff. Thanks for posting the fix.
>
> And "LBA" answers Duncan's disk concerns from earlier. It overcomes any
> worries about differing disk geometries should you want to do a "dd"
> directly from one disk to another.
>

No it doesn't.

Pick up 2 nGB disks from different manufacturers and you will
almost certainly find they are both ~ nGB but not quite the same.

Disk 1 may have 2000010 blocks while disk 2 has 2000000.  Thus if you dd 1->2 you
won't have anywhere to put those last 10 blocks and you could lose data.
Also you've just dd'd over a partition table which says the disk is bigger than it
actually is.

This is also a problem if you are replacing disks in a RAID array.
You have to make sure the new disks is >= the size of the old disk or you're
asking for trouble.  This is quite difficult as most manufacturers advertise
disks the nearest large unit (GB, MB etc) not actual size.

By the way, when you dd'd between your disks did you do anything about the badblocks list ?
Certainly ext[23] and reiserfs maintain internal lists for these and you will have dd'd them
along with everything else. Those blocks may not be bad on the second disk, but others
underlying your newly copied data might be....

Have fun,
Duncan

-- 
Duncan John Fyfe          X-ray Astronomy Group,
                          Dept. of Physics & Astronomy,
Phone +44 116 252 3635    University of Leicester,
E-mail djf at star.le.ac.uk  University Road,
                          Leicester, LE1 7RH, U.K.