[GRLUG] duplicate usb drive

[Michael Mol]

On 8/30/06, Bill Littlejohn <billl at mtd-inc.com> wrote:
>
>  I'm a little confused.
>  "You can correct the partition table with parted or fstab after it's
> done.".
>  What do you mean by "correct"?
>  I've used guiparted in Knoppix but not much else. I usually use Partition
> Commander.

That's what he's referring to. (Though I'm not sure your version of
parted supports resizing NTFS.  Not all do...I'm not sure any do.)

>  I'm also a little confused on the purpose of using fdisk and ntfsresize
> after transferring the image.

If the target drive is larger than the source drive, you may want to
expand your filesystem to take advantage of the extra space.  Before
you can run ntfsresize, the partition the NTFS filesystem resides on
has to be expanded.  That's what fdisk is for.

You could also use fdisk to create a new partition in the empty space,
and use Windows to create an NTFS partition on that.

Finally, you could just stick with a straight dd, and not bother with
that extra space.  Whatever works. :)

>
>  "
>  dd if=/dev/sda of=/dev/sdb bs=4000000
>  fdisk /dev/sdb
>  ...
>  ntfsresize /dev/sdb1
>  "
>  I know I'm being somewhat dense here - a little hand-holding would be
> appreciated.

* dd
"if" points to the input file
"of" points to the output file

...but you probably knew those.

"bs" allows you to specify the block size.

When dd copies data, it does it a certain number of bytes at a time.
When the Linux kernel copies data, it also processes data a certain
number of bytes at a time.  There's a little bit of overhead each time
dd or the Kernel processes a new block of data, which slows down the
transfer a little bit.

We can't control how much data the Kernel processes, since that's
device-specific.  We can, however, tell dd to processes data in block
sizes specified by "bs".  By doing that, we significantly reduce the
fragmentation of the operation in user space.

Ideally, we would want dd and the kernel to process data in same-size
chunks, but it's non-obvious exactly how much data the kernel is
willing to process at once. (And that's called an "atomic" operation,
for what it's worth. I seem to recall a number of 2KB, from somewhere
in the glibc info pages, but that was a long time ago.)

$ dd if=debian/boot.bin of=/dev/fd0 bs=512

The above command line would copy data out of a Debian boot floppy
image and write it to the floppy device, 512 bytes at a time.

$ dd if=/dev/sda of=/dev/sdb

The above command line would copy data from /dev/sda to /dev/sdb.  We
didn't specify a block size, so I don't know how many bytes it will
transfer at a time.  However, it will continue to transfer data until
it exhausts /dev/sda, or until it runs out of space on /dev/sdb.

>  :)
>  Bill

Mike

-- 
:wq