cli guru needed

[Patrick O'Callaghan]

On Sun, 2009-08-02 at 14:38 -0400, Robert P. J. Day wrote:
> On Sun, 2 Aug 2009, Patrick O'Callaghan wrote:
> 
> > On Sun, 2009-08-02 at 12:54 -0500, Mikkel L. Ellertson wrote:
> > > Bazooka Joe wrote:
> > > > Is there a way to combine these 2 commands to cut my time in half?
> > > >
> > > > VBoxManage internalcommands  converttoraw file.vdi file.raw
> > > > then I have to run
> > > > dd if=file.raw of=/dev/sdb
> > > >
> > > > -thx
> > > >
> > > You can can command on the same command in several ways. It depends
> > > on what you put between the command.
> > >
> > > ; - always run the next command.
> > > && - run the second command only if the first command is successful.
> > > || - run the second command if the first one fails.
> >
> > How is this going to reduce his total time? The commands are still
> > running sequentially.
> 
>   i'd bump up the blocksize of that dd command.  IIRC, the default
> blocksize for dd is 512 bytes -- painfully small and resulting in lots
> and lots of little writes.  crank up the blocksize significantly and
> that second command should speed up noticeably.

That's often true, but it depends a lot on the natural blocksize of the
target device. Also, if it's something like a pendrive it doesn't seem
to make any difference, given as most of the time is spent in kernel
buffers anyway (even the fastest are a lot slower than RAM and they
don't use DMA).

poc