Help, my disk array has one dead member

[Bruce Ferrell]

On 03/21/2017 07:06 PM, Kevin O'Gorman wrote:
> I need a quick bit of advice.
>
> I have a stripe array under mdadm, and one of the disks is dead or dying.  Nevertheless, there's a bunch of stuff that is NOT gone, and I'd like to capture all I can before I 
> even power this thing off.
> I'm missing some inodes, as well as some file and directory blocks.
>
> It's all hobby stuff, and it's all rebuildable, but I'd like to capture all the clues I can.
>
> I'm looking for a way to copy the whole directory structure, just omitting any file or directory that reports an error in the process.  I'll do it with find(1) if I have to, but 
> I'm wondering if there's a utility that's easily adapted to this situation.  Partial directories are okay.  Partial files are not.
>
> -- 
> Kevin O'Gorman
> #define QUESTION ((bb) || (!bb))   /* Shakespeare */
>
> 	Please consider the environment before printing this email.
>
>
>
Kevin,

Yes, it's a good idea to make a copy of the file system before doing irrevocable things,  but depending on how the RAID was set up it's either needless (this is why we use a RAID) 
or irrelevant.

I can say that with good authority because I daily work on appliance systems the use md raids that often fail drives.

Simple raid0 is destroyed with a member drive or partition out so no copy is needed/possible.  raid1, your data is intact on one (or more) of the mirrors and a copy is nice, but 
not necessary (tar will work on the file system mounted to the md).

There are some decent how-tos that I use when needed:

http://www.tjansson.dk/2013/12/replacing-a-failed-disk-in-a-mdadm-raid/

http://www.ducea.com/2009/03/08/mdadm-cheat-sheet/

I use the cheat sheet a lot.