2015-12-15 14:44 GMT+01:00 Phil Turmel [off-list ref]:

On 12/15/2015 06:30 AM, TheGerwazy . wrote:

quoted

The main problem is the data offsets are not stored elsewhere than in
superblock. I have some drives from debian 6.0.5 and some were changed
in debian 7.5. In 6.0.5 default data offset was at 2048 sector while
int 7.5 it is 262144.

There have been other defaults, and various adjustments to the
algorithms that handle special cases.  The purpose of the superblock is
to store the data needed by the features supported.  Where else
would/could you store this information?

maybe mdadm.conf, maybe syslog ?
It the same problem like partitions, ext3 superblocks
We need only a few parameters to recover whole array - some of them we
could guess.
Meybe its a good idea to spare some backups of mdadm superblock like in EXT3 ?

Even though mdadm is, in my opinion, reliable system and I suggest it
to my clients because of easy recovery.

This highlights why --create is such a terrible way to recover an array,
and highlights the danger posed by well-intentioned bloggers who
cavalierly suggest using it.

Pretty much everyone who comes here for advice *before* trying --create
has been successfully helped.  The results after --create are decidedly
mixed.

Due to that there are production systems, sometimes there is no time
to wait even an hour for advice - your boss would ask you "I need my
data, why you are waitng ?"
Another problem is when you are asking on the Internet - you sometimes
receive completly wrong advice what lead you to losing the data...

quoted

Thanks for Phil

You're welcome.

Phil

Best regards, Gerard