Re: cloning to multiple drives with the "dd" command.

[didier chavaroche]

> Message du 19/02/15 22:56
> De : "Bob Proulx" <address@hidden>
> A : "didier chavaroche" <address@hidden>, address@hidden
> Copie à :
> Objet : Re: cloning to multiple drives with the "dd" command.
>
> Bernhard Voelker wrote:
> > didier chavaroche wrote:
> > >Executing the "dd" command 23 time leads to transfert rate too low
> >
> > Just to be clear (as you didn't show us the commands executed):
> > how did you execute the dd command 23 times?
> > In parallel, e.g. a background processes?
>
> I was wondering that as well.
>
> Without really knowing what you are doing if it were me not quite
> knowing what I was doing I might keep a copy of the source disk in a
> tmpfs ram file system and ensure there is enough ram to host it
> without swapping. That would reduce the I/O needed for the source
> reducing it to ram accesses.
>
> There is still a bottleneck on the outgoing I/O however. I expect
> that you are completely saturating the bus bandwidth. If I were doing
> that I would consider using multiple systems in order to gain parallel
> bus bandwidth. I would read the source data from the net and write to
> the multiple devices spread out over multiple systems.
>
> Bob
>

 

The way I use the dd command is the following:

I developped a JAVA application which in a thread class call a script with two arguments SOURCE & TARGET.

 

In this script I use the command "sudo dd if=SOURCE of=TARGET bs=4096 conv=notrunc,noerror &"

Then the script identify the PID of the dd command and send every 5 seconds the -USR1 signal throught kill
to print out the progress.

 

progress which is feedback to my JAVA application that calculate the total  progress and the transfert rate.

 

And of course there are as many threads as targets, maximum 23.

 

Thank you for your advice.

 

Regards

Didier