How to optimize the cloning of a disk with a big empty ext3 partition?

[Gregoire Gentil]

On Fri, 2009-06-19 at 21:33 -0400, Theodore Tso wrote:
> On Fri, Jun 19, 2009 at 04:42:54PM -0700, Gregoire Gentil wrote:
> > Hello,
> > 
> > I need to duplicate a huge number of identical 8GB SD cards on which I
> > have 1GB of data at the beginning of the disk on various partitions and
> > then a 7GB ext3 partition which is rather empty (just a few MB of data).
> > 
> > The duplicator device enables me to select which sectors I can
> > binary-duplicate. I would love to divide by 8 my duplication time, by
> > duplicating only the first GB and then the beginning of the 7GB ext3
> > partition.
> > 
> > When I do a mkfs.ext3, I see that the super-block is written to various
> > locations of the partition which is not good for the optimization I
> > would like to do.
> 
> The metadata for ext3 is scattered across the disk; it's not just the
> superblock, but it's also parts of the inode table, and bitmap
> allocation blocks, which must be initialized.
> 
> It's possible to determine the list of blocks that need to be
> initialized, but it's going to be a rather long list.  If you need to
> type the list of sectors into your duplicator, it's probably not
> practical.  If on the other hand you can feed it a file with a set of
> sector numbers, you could extract that list of blocks in use from the
> filesystem (which listed by dumpe2fs, although not in the most
> convenient format), and convert it to sector numbers counting from the
> beginning of the disk (as opposed to block numbers counting from the
> beginning of the partitions), and then feed the whole long list of
> sector block ranges to your duplicator device.
> 
> 						- Ted
Ted,

Many thanks for the explanation. It's what I was afraid of!

Grégoire