Re: [gentoo-user] Preserving the initial partionin/formatting of an usbstick

Mick <michaelkintzios@×××××.com> [16-03-30 17:12]:
> On Wednesday 30 Mar 2016 05:28:29 Meino.Cramer@×××.de wrote:
> > Mick <michaelkintzios@×××××.com> [16-03-30 03:56]:
> > > On Tuesday 29 Mar 2016 19:53:45 Meino.Cramer@×××.de wrote:
> > > > The real thing:
> > > > The usbstick has a partition table, which was the reason to ask
> > > > for a way to preserve it.
> > >
> > > OK, I wasn't sure if it did.
> > >
> > > In this case as I suggested, fdisk will show you the number and size of
> > > partitions.  minfo will show you the geometry of the partition, should you
> > > wish to manually recreate it in the future.  However, there are tools to
> > > help avoid manual partitioning!  ;-)
> > >
> > > To answer exactly what you asked, copy the partition table (assuming all
> > > the USB stick contains is a single primary partition) by using good ol'
> > > dd:
> > >
> > > dd if=/dev/sdX of=~/mbr.img bs=512 count=1
> > >
> > >
> > > Reverse the command to paste the MBR and partition table back.  That
> > > should
> > > bring you back where you started when you first bought the USB stick.  If
> > > for some weird reason the USB stick partitioning scheme included extended
> > > and logical partitions, then read one additional step below.
> > >
> > > > Again my questions:
> > > > Where are the partioning/format defining on the device?
> > > > If there are only stored the beginning of the device: How
> > > > much do I need to copy?
> > > > If there are tools to extract all needed informations of the
> > > > partioning/formatting and to recreate exactly that kind of
> > > > partitioning/formatting later with that or other tools:
> > > > Which tools do I need and how to use them?
> > >
> > > First copy the MBR and partition table using dd as I suggested above.
> > > Then
> > > use sfdisk --dump to create a text file with information on the size and
> > > positioning of the remaining partitions.
> > >
> > > sfdisk --dump /dev/sdX > sdX.dump
> > >
> > >
> > > To restore first run dd in the reverse order:
> > >
> > > dd if=~/mbr.img of=/dev/sdX bs=512 count=1
> > >
> > > Then change the file director on the sfdisk --dump command:
> > >
> > > sfdisk --dump /dev/sdX < sdX.dump
> > >
> > > Needless to say you will need both 'mbr.img' and 'sdX.dump' files to
> > > restore the drive partitioning scheme to its original state, if it
> > > contains more than one primary partition.  When you are restoring the
> > > partition tables, double check the /dev/sdX name or you could damage some
> > > other disk in your system!
> > Hi Mick,
> >
> > yeah! That's the informations I needed! Great, thank you.
> >
> > By the way, somehow "half offtopic":
> >
> > In the past I did hd-cloning (full contents, not only partition
> > schemes etc.) with dd. For a 1TB-disk this tooks quite a while.
>
> I think by default dd will use bs=512 which will take forever when copying a
> large drive.  In this case increase the block size to something more
> reasonable, like e.g. bs=4096.
>
> > Then I came accross an article, which uses "pv" for that purpose:
> >
> > pv < /dev/sda > /dev/sdb    (as root...;)
> >
> > THAT was fast!
>
> PV probably uses larger block sizes by default.  You could test this with a
> known file size and compare the transfer time between dd and pv.
>
>
> > I mentioned it here, because (may be) someone else wants to copy/clone
> > a complete flash drive for backup purposes for example and may
> > experience an increase speed with pv instead of dd.
> >
> > If one wants to copy only parts, dd is the winner.
>
> Also worth mentioning is dcfldd which unlike dd can show progress of the bit
> stream and also produce hashes of the transferred output.  It has the same
> performance as the dd command though.
>
> --
> Regards,
> Mick

 I had experimented a lot with the block size argument of dd
 previously and it seems I never had find the sweet spot. May it was
 simply an blind and unfortunate dance around it...who knows.
 pv did it right from the beginning the correct way with a super
 simple command: pv < /dev/sda > /dev/sdb
 :)

 I installed dcfldd just a momnent before and will experiment with it 
 - thanks for mentioning it!

 By the way:  For what stands the 'dd' for ?
 (Think unix!)

 :)

 Best regards
 Meino