Re: A partially failing disk in raid0 needs replacement

["Austin S. Hemmelgarn" <ahferroin7@gmail.com>]

On 2017-11-14 07:48, Roman Mamedov wrote:
> On Tue, 14 Nov 2017 10:36:22 +0200
> Klaus Agnoletti <klaus@agnoletti.dk> wrote:
> 
>> Obviously, I want /dev/sdd emptied and deleted from the raid.
> 
>    * Unmount the RAID0 FS
> 
>    * copy the bad drive using `dd_rescue`[1] into a file on the 6TB drive
>      (noting how much of it is actually unreadable -- chances are it's mostly
>      intact)
> 
>    * physically remove the bad drive (have a powerdown or reboot for this to be
>      sure Btrfs didn't remember it somewhere)
> 
>    * set up a loop device from the dd_rescue'd 2TB file
> 
>    * run `btrfs device scan`
> 
>    * mount the RAID0 filesystem
> 
>    * run the delete command on the loop device, it will not encounter I/O
>      errors anymore.
While the above procedure will work, it is worth noting that you may 
still lose data.
> 
> 
> [1] Note that "ddrescue" and "dd_rescue" are two different programs for the
> same purpose, one may work better than the other. I don't remember which. :)
As a general rule, GNU ddrescue is more user friendly for block-level 
copies, while Kurt Garlof's dd_rescue tends to be better for copying at 
the file level.  Both work fine in terms of reliability though.