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

[didier chavaroche]

> Message du 20/02/15 11:48
> De : "Bernhard Voelker" <address@hidden>
> A : address@hidden, "Mike Hodson" <address@hidden>
> Copie à : "didier chavaroche" <address@hidden>, "Coreutils" <address@hidden>, "Bob Proulx" <address@hidden>
> Objet : Re: cloning to multiple drives with the "dd" command.
>
> On 02/20/2015 11:04 AM, Sami Kerola wrote:
> > Is there a reason why
> >
> > $ dd if=/dev/zero count=1 of=/tmp/a of=/tmp/b
> >
> > could not be made to write to two, or any number of of= destinations,
> > in single execution?
>
> Because we have tee(1)
>
> dd if=$SOURCE $I_OPTS \
> | tee \
> >( dd $O_OPTS of=$TARGET1 ) \
> >( dd $O_OPTS of=$TARGET2 ) \
> >( dd $O_OPTS of=$TARGET3 ) \
> >( dd $O_OPTS of=$TARGET4 )
>
> Getting the errors of the writing dd processes would
> be a bit hard though.
>
> Anyway, this doesn't avoid the IO bottleneck, it just avoids
> to read $SOURCE n-times. IMO having more than 3-4 dd's in
> parallel is only slowing down the whole process. Maybe the
> 'nochache' flag could help to avoid flooding the system cache
> at least.
>
> Have a nice day,
> Berny
>

Hello everybody.

 

Ok, I recognize trying to clone 23 disks a once can be a little bit hard for my system.

It is giving a hard time to the disk cache.

But why can't I do it like in 2 or 3 step. cloning 8 drives at once, then another 8 then another 8.

I tried this way and cloning the first 8 works fine I have a transfert rate about 100MB/s.

But then for the second part, cloning the 8 drives leads to a transfert rate about 20MB/s.

 

I don't understand why the cache is stil so trashed after cloning disks.

Is there a way to restore or clean it so I have a Transfert rate about 100MB/s on all my cloning steps?

 

Thanks

 

Regards

 

Didier