[olug] using dd to clone a drive

[Kevin]

Rob has a good point about other hardware being bad, too. Maybe something
like this: `dd if=/dev/sda of=/dev/null` as a test for reading the disk?

On Wed, Apr 20, 2016 at 7:35 PM, Rob Townley <rob.townley at gmail.com> wrote:

> echo Kevins trick to get feedback from dd.
>
> *There is also dd_rescue (note the underscore).  At least one of them reads
> the drive forwards and backwards.  One is not compatible with '|' pipes.
>
> *Make sure you execute `sync` as root and wait for it to finish.
>
> *Keep in mind the destination disk or USB channel may be bad as well, so
> maybe try copying to the harddisk first.
>
> * ddrescue will NOT read AudioCDs!  Mount it first.
>
> On Wed, Apr 20, 2016 at 11:24 AM, Christopher Cashell <topher-olug at zyp.org
> >
> wrote:
>
> > On Tue, Apr 19, 2016 at 10:16 AM, Justin Reiners <justin at hotlinesinc.com
> >
> >  wrote:
> >
> > > ddrescue is great, I use it all the time. Hih
> > > On Apr 19, 2016 9:50 AM, "Matthew G. Marsh" <olug4mgm at paktronix.com>
> > > wrote:
> > > > +1 on that. I actually install this as dd on my systems as the syntax
> > for
> > > > basic work is pretty much the same and the extra error correcting
> > > features
> > > > are well worth it. Especially when you use it over a netblock
> > connection.
> > > >
> > > > mgm
> > > >
> > > > On Mon, 18 Apr 2016, Dan Linder wrote:
> > > > If you're looking to save the data that might be in the bad sectors,
> > use
> > > >> "ddrescue".  It's restart-able and has options to intensely try the
> > > failed
> > > >> sectors.
> > > >>
> > > >> Dan
> > >
> >
> > To follow on the comments from Dan and others, dd will usually work, and
> > has the advantage of being installed on almost every box.  However, there
> > are better tools that are worth looking at if available.
> >
> > There are at least half a dozen dd-like tools[1] that handle disk errors
> > and bad sectors better than dd.  Many of them perform better, too,
> > defaulting to larger block sizes.  The better versions will start with a
> > large block size, and then reduce it repeatedly if they run into
> problems,
> > minimizing lost data, and maximizing recovered data.  Most of them give
> > better visibility into status, too.
> >
> > Another thing that can be handy is to use dd to copy the disk to a disk
> > image file.  That image file can then be mounted via loopback for
> accessing
> > the data.  This can be easier to work with and manage than trying to go
> > straight from one drive to another drive.
> >
> > One potential issue with traditional dd is that if it runs into a block
> it
> > can't read, it can get hung on certain disk errors trying to read data.
> > Many of the dd replacements will set a timeout after which they'll reduce
> > the block size and retry, or eventually give up and move on.
> >
> > For a 1GB drive, if any copy hasn't finished in a couple of hours, it's
> > unlikely it will finish.  Try a different dd replacement that handles
> > errors better and see if that works for you.
> >
> > Note, also, that dd can be used on a full disk (i.e. /dev/sda) or on a
> > partition (i.e. /dev/sda1).  Depending on what your goal is, one or the
> > other might be more appropriate.
> >
> >  [1] Quick list of packages from a Debian box: dcfldd sdd ddpt dc3dd rdd
> > myrescue gddrescue safecopy
> >
> > --
> > Christopher
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