Re: How to recover after md crash during reshape?

[Phil Turmel <philip@turmel.org>]

Good morning Neil,

On 10/20/2015 09:35 PM, Neil Brown wrote:

> Nothing dumb about that - you don't need a --backup option.
> If you did, mdadm would have complained.
> 
> You only need --backup when the size of the array is unchanged or
> decreasing.

> mdadm reads the first few stripes and stores them somewhere in each of
> the spares.  md (in the kernel) then reads those stripes again and
> writes them out in the new configuration.  It appears that one of the
> writes failed, others might have succeeded.  This may not have corrupted
> anything (the first few blocks are in the same position for both the old
> and new layout) but it might have done.

> If you do want to look for the backup, it is around about the middle of
> the device and has some metadata which contains the string
> "md_backup_data-1".  If you find that, you are close to getting the
> backup data back.

Hmmm.  This feature has advanced beyond my last look at the code.  I was
under the impression the backup option was only optional when mdadm
could move the data offset.  Does this new algorithm apply to v0.90
metadata, a v3.2 kernel, and v3.2.5 mdadm?

Phil