[clug] Recovering data from old disks. Max age observed?

steve jenkin sjenkin at canb.auug.org.au
Sun Jun 16 08:46:18 UTC 2019

> On 15 Jun 2019, at 23:02, George at Clug via linux <linux at lists.samba.org> wrote:
> Not having used ddrescue, if you have time, please do explain the above, particularly what rescue-sdX.dd rescue-sdX.map are ? (Rescued image file and log file?)
> What do you do with the image file?  Can you mount it to check if it is readable?  If so, how?


normal caveats apply:

	this is systems admin task and making mistakes, especially with source & destination,
		can be catastrophic to your system.
	Unix tools are “sharp” - you can damage/ break things easily and without recovery or query.
	If those constraints don’t work for you, find, or write, safer tools to do what you need.

In answer to your question, search for this term or similar (found lots of useful pages):

	linux using "dd" to create disk images

You can make images of CD & DVD’s (iso’s), for example, to burn Distributions to CD or USB stick - bootable or not.

This is possible because Unix/ Linux does two things:

	- everything is a ‘file’, including raw devices
	- devices have names in the filesystem (/dev/sda1, /dev/cdrom, …)
		and can be read & written like any file, with a few caveats.
		provided you have permission - normally use ’sudo’.

There’s probably four useful things you can do when making or using an ‘image’:

	- copy to an identical disk or partition
		[see caveat - dangerous, have to be sure what you’re doing & be prudent ]

	- copy a whole device or partition to a _normal_  file to use later.
		- can “loop back” mount this image and examine it, even use it, as a mounted volume.
		- can “image” (write/ create) new drives or CD’s from this copy
		- can attach to a Virtual Machine (as either a Disk Drive or ISO image)

‘ddrescue’ attempts to do some of the same tasks as ‘dd’ - but as the name says, it is for _rescuing_ data from media throwing errors. I’ve never used ‘ddrescue’ as my first approach, but then again, I’m a newcomer to it.



Steve Jenkin, IT Systems and Design 
0412 786 915 (+61 412 786 915)
PO Box 38, Kippax ACT 2615, AUSTRALIA

mailto:sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin

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