Sorry to not be precise enough
here are the command and result i tried:
# mdadm --re-add /dev/md0 /dev/sdb1
mdadm: --re-add for /dev/sdb1 to /dev/md0 is not possible

# mdadm --add /dev/md0 /dev/sdb1
mdadm: /dev/sdb1 reports being an active member for /dev/md0, but a
--re-add fails.
mdadm: not performing --add as that would convert /dev/sdb1 in to a spare.
mdadm: To make this a spare, use "mdadm --zero-superblock /dev/sdb1" first.

Also i check my disk and seem ok :
#smartcll -l selftest /dev/sdb1
=== START OF READ SMART DATA SECTION ===
SMART Self-test log structure revision number 1
Num  Test_Description    Status                  Remaining
LifeTime(hours)  LBA_of_first_error
# 1  Extended offline    Completed without error       00%     14046         -
# 2  Short offline       Completed without error       00%     14041         -


Thanks for helping me

On Mon, Mar 31, 2014 at 10:28 AM, Mikael Abrahamsson [off-list ref] wrote:

On Mon, 31 Mar 2014, bobzer wrote:

quoted

so there i tried to re-add the disk that doesn't works

"Doesn't work" isn't a helpful problem description. Please provide output
from dmesg when you do this, error message (if any) from CLI, what command
you tried with, etc.

--
Mikael Abrahamsson    email: swmike@swm.pp.se