I'm trying to create a new Raid 5 array on my system using 3 12TB Seagate Exos drives on a Ubuntu Server 18.04 install. At first I just tried to use Webmin and created a GPT partition on each of the drives then tried to create an array but it immediately started in degraded mode while still showing all three disks still in the array. I looked at the log in kern.log and it showed the array was active with 2 out of 3 devices and was in recovery mode.
That didn't seem right so I deleted the array and tried at the command line. I used fdisk to re-create the patriation table and tried to create the raid using the following command:
~$ sudo mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/sda /dev/sdb dev/sdd
and got the following return:
mdadm: layout defaults to left-symmetric mdadm: layout defaults to left-symmetric mdadm: chunk size defaults to 512K mdadm: partition table exists on /dev/sda mdadm: partition table exists on /dev/sda but will be lost or meaningless after creating array mdadm: partition table exists on /dev/sdb mdadm: partition table exists on /dev/sdb but will be lost or meaningless after creating array mdadm: cannot open dev/sdd: No such file or directory
I tried changing the SATA cables and SATA ports thinking that could be a problem but that wasn't it. I thought it was initially a bad disk but as I switched SATA ports the drive that was left out would occasionally change (verified by checking serial numbers) so I'm at a loss as to what could be causing this and had hope someone knew what was going on and could help.
Here is what Webmin shows:
Device file /dev/md0 UUID 6981f19f:731e442b:f8c8e8e2:c47a8729 RAID level RAID5 (Distributed Parity) Filesystem status Active but not mounted Usable size 23437503488 blocks (21.83 TB) Persistent superblock? Yes Layout left-symmetric Chunk size 512 kB RAID errors 1 disks have failed RAID status clean, degraded, recovering Rebuilding progress 0 % (1447.9 min, 131 MB/s) Partitions in RAID SATA device A partition 1 SATA device B partition 1 SATA device D partition 1