Mount a HDD from a RAID to recover some data

I'm struggling to mount a HDD from a Synology DS214 RAID1 on my computer to backup some data from it.

I can't mount directly because this HDD come from a raid

mount /dev/sda1 /mnt
mount: unknown filesystem type 'linux_raid_member'

So i installed mdadm on my computer (Debian Buster) and --force assemblage

mdadm --assemble --run --force /dev/md/2 /dev/sda1
mdadm: failed to add /dev/sda1 to /dev/md/2: Invalid argument
mdadm: failed to RUN_ARRAY /dev/md0: Invalid argument

dmesg :

md: sda1 does not have a valid v1.2 superblock, not importing!
md: md_import_device returned -22
md: md2 stopped.

I tried :

mdadm --assemble /dev/md/2 /dev/sda1 --update=summaries --force
mdadm: --update=summaries not understood for 1.x metadata

and :

mdadm -A --update=name /dev/md/2
mdadm: failed to add /dev/sda1 to /dev/md/2: Invalid argument
mdadm: failed to RUN_ARRAY /dev/md/2: Invalid argument

I'm not sure what to do now, i'm a little bit scared to do a rookie mistake, so i looking for help

Thanks in the first place !

Additionnal informations / config files

mdadm.conf (default file from the installation)

ARRAY /dev/md/2  metadata=1.2 UUID=a3377871:9ad25389:8c66cfb8:c817e2fb name=Toto:2

mdadm --examine /dev/sda1
/dev/sda1:
          Magic : a92b4efc
        Version : 1.2
    Feature Map : 0x0
     Array UUID : a3377871:9ad25389:8c66cfb8:c817e2fb
           Name : Toto:2
  Creation Time : Thu Jan 14 23:27:30 2021
     Raid Level : raid1
   Raid Devices : 2

 Avail Dev Size : 7804374912 (3721.42 GiB 3995.84 GB)
     Array Size : 3902187456 (3721.42 GiB 3995.84 GB)
    Data Offset : 2048 sectors
   Super Offset : 8 sectors
   Unused Space : before=1968 sectors, after=18446744073709549576 sectors
          State : active
    Device UUID : ba6a147f:f7fd9089:914e6307:789bc8c4

    Update Time : Fri Jan 15 07:18:55 2021
       Checksum : 4a48baac - correct
         Events : 2


   Device Role : Active device 1
   Array State : AA ('A' == active, '.' == missing, 'R' == replacing)

You need to specify that a device is missing with the missing keyword. For example:

mdadm --assemble --run --force /dev/md/2 /dev/sda1 missing

I solved my issue using the following commands : mdadm.conf :

DEVICE partitions
ARRAY /dev/md/2 level=raid1 num-devices=2 devices=/dev/sda1,missing

reboot

mdadm --assemble --run --update=devicesize /dev/md/2
cat /proc/mdstat
mdadm -Asf && vgchange -ay
lvchange -ay /dev/vg1000/lv
mount /dev/vg1000/lv /mnt

Source :

• Wüstengecko on unix.stackexchange - "md raid5: “no valid superblock” but mdadm --examine says everything is fine"
• Synology FAQ "How_can_I_recover_data_from_my_DiskStation_using_a_PC"