[GTALUG] Advice request

[D. Hugh Redelmeier]

| From: Lennart Sorensen <lsorense at csclub.uwaterloo.ca>

| On Thu, Jul 16, 2015 at 11:57:49AM -0500, o1bigtenor wrote:
| > 
| > I have a large system with a fair number of resources which has just come
| > home from the hospital (computer) when I had a disk drive fail abruptly.
| > 
| > 1.The tech tells me that the hard drive can be accessed. How do I do a low
| > level transfer to another hard drive?
| > (This would mean that I would have empty sectors but there is some
| > information that I would like to get.)

DON'T make any sudden moves.  They are likely to be wrong since you
are upset and you are doing something new.
 
| ddrescue can be handy for taking an image of a slightly defective
| disk to somewhere else, so that you can then experiment on the copy to
| recover things.

Yes, I do this:

1) raw ddrescue from the whole failing disk to a whole new disk.  (Make
sure that the new disk is at least as large as the old one!)  By
copying the whole disk, you get the partition table and boot blocks.
But you also get the same UUIDs so it is best to not have the two
disks on the same machine after the copy is done (mount etc. will be
confused).

2) Then put the failing disk on a shelf

3) Then play with the new disk.

I find it best to do this from a live USB stick or CD so I'm not
acutally booting off the bad hard drive, the new hard drive, or even
just the same controller.

Make sure that the live system does not use the sick disk's swap
partition.

Note: ddrescue is a bit tricky, but it is brilliant.  Read the manual
twice before using it.  Google for examples of usage.  I've posted to
this list messages about how to use it.  You DO want to let it use a
logfile!

Somewhere in there I do a
	smartctl -x /dev/sda
and capture the output somewhere on another machine.  I want to ask
the drive what it thinks is going on.

BTW, keep in mind that the identification of the problem is
provisional.  Subsequent observations may point the finger elsewhere.
Eg. power supply, disk controller, RAM, sunspots.