[Discuss] RAID question

[Alan W. Irwin]

On 2016-04-30 16:05-0700 Patrick wrote:

> Hi.  :-)
>
> Does anyone know if there's a Linux utility for drive cloning,
> which compares two drives and *only* writes changes to the
> destination drive where it finds differences?  Using dd would
> also work, but would end up doing a lot of unnecessary work in
> the process [and performing a lot of unnecessary writes].
>
> I had this idea to build a hardware RAID 1+0 array using SD
> cards and some junk off eBay, but maintaining it if/when a card
> fails could get interesting...  It would also be convenient if
> I could remove a single RAID 0 drive, use it for a while, then
> reintroduce it [with changes] to the mirrored 1+0 array.
>

Hi Patrick:

Interesting question but could you clarify your motivation here?  Is
this to avoid unnecessary writes so as to avoid write wear on your SD
cards?

I did a google search using the terms <rsync raw disk blocks>, and 
got a lot of hits for similar ideas, but I think the consensus (just
from reading the google summaries and not actually looking deeper)
seemed to be this is outside the scope of rsync.  But if you read
deeper you might find something interesting.

Another google search I did was for the terms <dd ssd> and there are
apparently some tricks you have to be aware of even if you are willing
to accept the write wear.

Alan

__________________________
Alan W. Irwin

Astronomical research affiliation with Department of Physics and Astronomy,
University of Victoria (astrowww.phys.uvic.ca).

Programming affiliations with the FreeEOS equation-of-state
implementation for stellar interiors (freeeos.sf.net); the Time
Ephemerides project (timeephem.sf.net); PLplot scientific plotting
software package (plplot.sf.net); the libLASi project
(unifont.org/lasi); the Loads of Linux Links project (loll.sf.net);
and the Linux Brochure Project (lbproject.sf.net).
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