I have a RAID5 on SYnology nas system that has crashed. In first the system prevent to one disk has been removed from the raid with the degraded status. After a shudown to unplug the disk and restart the nas, the raid status has changed to failed (CLean, degraded satus is still visible in raid configuration of mdadm) but in gui the size of raid array is 0byte :( and impossible to repair this!
closed as unclear what you're asking by roaima, Jeff Schaller♦, telcoM, Mr Shunz, Thomas Jan 21 at 11:00
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Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] md2 : active raid1 sda3 sdb3 21392384 blocks super 1.2 [2/2] [UU] md3 : active raid5 sdd5 sdh5 sdg5 sdf5 sde5 9743376960 blocks super 1.2 level 5, 64k chunk, algorithm 2 [6/5] [_UUUUU] md1 : active raid1 sda2 sdb2 sdd2 sde2 sdf2 sdg2 sdh2 2097088 blocks [12/7] [UU_UUUUU____] md0 : active raid1 sda1 sdb1 sdd1 sde1 sdf1 sdg1 sdh1 2490176 blocks [12/7] [UU_UUUUU____] unused devices: <none>
It's a good thing
mdadm --create errored out on you: that command is more likely to destroy your array than save it. Since it failed early, it likely didn't do any damage.
/dev/md3 is only missing one device, so it should be possible to recover it. Running
mdadm --run /dev/md3 followed by
mdadm --readwrite /dev/md3 should make it usable; at this point, replace the failed disk and add the new one to the array with
mdadm --manage /dev/md3 --add /dev/<insert new disk here>. The
md subsystem will then start rebuilding the array.