In the NAS kit "ReadyNAS RN212" made by NetGear, I took out the drive used in JBOD mode from the main body.
Later, when I tried to retrieve data by connecting with a USB conversion cable etc., I ended up struggling with software RAID (mdadm) for some reason, so I will record a solution for those who have fallen into a similar situation.
--Working environment: ReadyNAS 212 main unit
--Connect the HDD to the front USB terminal
--You can log in as root with SSH working
--Extracted disk: / dev / sdc
--Area you want to retrieve: / dev / sdc3
--Mount point: / mnt / test
Even if the drive is built with JBOD, it will be built as ** 1 RAID1 ** on ReadyNAS. Therefore, if you want to mount it on another machine, you need to reconfigure RAID1.
~# fdisk -l /dev/sdc
Disk /dev/sdc: 2.7 TiB, 3000558944256 bytes, 5860466688 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: gpt
Disk identifier: ***************************************
Device Start End Sectors Size Type
/dev/sdc1 64 8380487 8380424 4G Linux RAID
/dev/sdc2 8388672 9435207 1046536 511M Linux RAID
/dev/sdc3 9437248 5860270919 5850833672 2.7T Linux RAID <-Data area
~# mdadm -v --assemble --force --update=devicesize --run /dev/md13 /dev/sdc3
mdadm: looking for devices for /dev/md13
mdadm: /dev/sdc3 is identified as a member of /dev/md13, slot 0.
mdadm: added /dev/sdc3 to /dev/md13 as 0
mdadm: /dev/md13 has been started with 1 drive.
~# mkdir /mnt/test
~# mount /dev/md13 /mnt/test
~# ls /mnt/test
home Music Photo Temp Videos
When you connect to Windows, the partition information will be lost. I rescanned the partition with TestDisk, wrote it, and forced it again.
Thanks to @ TAKUMA327 for sharing information about mdadm on Twitter. Mirroring an existing single drive with a new drive on Linux was also very helpful.