Help, my disk array has one dead member

[Bruce Ferrell]

On 3/22/17 3:37 PM, Xen wrote:
> Bruce Ferrell schreef op 22-03-2017 22:36:
>
>> Simple raid0 is destroyed with a member drive or partition out so no
>> copy is needed/possible.
>
> He said that one of the drives was damaged, but still readable. The 
> other was fine.
>
Yes and he also said it's an md raid.  As I said, the devil is in the 
details;  If it's raid1 (or higher) and one of the elements is damaged, 
the others cover for that with speed degradation.

raid0, do NOT use any dd variant on the physical disk.  md has internal 
data structures on the physical disks and doesn't transplant well to new 
drives.

You *might* be able to get away with dd on the md device, but that is 
active and managed by the md subsystem.  I was taught NEVER use dd on 
active devices... Unless you want trash data.

Use tar and you may have to be selective about what you copy but then 
again maybe sector relocation can help you get past the damage for tar.

Where this get's REALLY dicey; damaged data may have been mirrored back 
to the good drive from the bad one.  NASTY!

Bottom line, one size never fits all...  poke, prod (gently) and use 
trouble shooting steps to make a determination of what's needed to 
recover and NEVER blindly follow "just do this..." instructions