Re: overlay file to test btrfs repairs

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

On 2016-03-21 05:55, Duncan wrote:
> Chris Murphy posted on Sun, 20 Mar 2016 21:43:52 -0600 as excerpted:
>
>> Hi folks,
>>
>> So I just ran into this:
>> https://raid.wiki.kernel.org/index.php/
> Recovering_a_failed_software_RAID#Making_the_harddisks_read-
> only_using_an_overlay_file
>
> [That's a single link, wrapped by my client.]
>
>> This is a device mapper overlay file - not overlayfs.
>>
>> For the repairs that are sometimes uncertain what's next, maybe this is
>> a viable option to avoid changing the file system? I'm thinking
>> chunk-recover might take up too much space, I'm not sure how that one
>> works, if chunks are just being read or if they have to be rewritten or
>> if it's just the chunk tree? But for 'btrfs check' and 'btrfs rescue
>> super-recover/zero-log' there should be very little being written so the
>> overlay idea might be a good step?
>>
>> Opinions?
>
> That's a creative and potentially quite useful possible solution to an
> often hairy problem.  Thanks for bringing it up. =:^)
>
> Provided Hugo and the devs don't find major fault with the idea, linking
> that from appropriate locations (as a possible solution in the Problem
> FAQ is the first one that occurs to me) in the btrfs wiki could be quite
> useful, to many.
>
If we could find some way to have the programs themselves do this if the 
system supports it (and the user opts in of course), it would be really 
helpful.  That said, I can see this possibly causing issues due to 
duplicate device UUID's.