Setting up RAID: Unknown mount point

Support
1

Dear all,

After installing Manjaro on an SSD I added two HDDs and set them up as RAID 10 following the Arch Linux guide

One step in this guide is:

mdadm --create --verbose --level=10 --metadata=1.2 --chunk=512 --raid-devices=2 --layout=f2 /dev/md/MyRAID10Array /dev/sdb1 /dev/sdc1

I altered the step into:

mdadm --create --verbose --level=10 --metadata=1.2 --chunk=512 --raid-devices=2 --layout=f2 /dev/md/media1 /dev/sda1 /dev/sdb1

The only difference is that I changed the mount point from /dev/md/MyRAID10Array into /dev/md/media1.

The RAID seems to be fine. sudo fdisk -l returns:

Disk /dev/sda: 1.82 TiB, 2000398934016 bytes, 3907029168 sectors
Disk model: WDC WD20EFRX-68A
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: D8FDDE3D-607C-1F4F-B096-25F18FE93387

Device Start End Sectors Size Type
/dev/sda1 2048 3906824191 3906822144 1.8T Linux RAID

Disk /dev/sdb: 1.82 TiB, 2000398934016 bytes, 3907029168 sectors
Disk model: WDC WD20EFRX-68A
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: 933A8718-9533-EB44-8F7B-CF5BB1B226E4

Device Start End Sectors Size Type
/dev/sdb1 2048 3906824191 3906822144 1.8T Linux RAID

…

Disk /dev/md127: 1.82 TiB, 2000157671424 bytes, 3906557952 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 524288 bytes / 1048576 bytes

Now my question: Why is the mount point /dev/md127 and not /dev/md/media1?
There is a link from /dev/md/media to /dev/md127. What are the mechanics behind it?

Thank for your help and best regards,
Fabius

2

Did you tweak your /etc/mdadm.conf file?

3

raids disks are always using theses internal mountpoint /dev/md12x (logical Raid mount point )
you should check with

cat /proc/mdstat
mdadm --detail /dev/md127

4
  1. /dev/md12x are raid devices.
  2. If you name such a device, there will be always a symlink.
  3. It is like /dev/sda1 could have a symlink to /dev/disk/by-label/label-of-partition-sda1
5

Thanks for your responses!

@ merlock:
The non-comments in /etc/mdadm.conf read:

DEVICE partitions
ARRAY /dev/md/media1 metadata=1.2 name=feynman:media1 UUID=fdbab225:d014b874:8d0a50de:b9c94b2b

I added the portion “ARRAY … b2b” by

sudo mdadm --detail --scan >> /etc/mdadm.conf

@ stephane:
cat /proc/mdstat returns:

Personalities : [raid10]
md127 : active raid10 sda1[1] sdb1[0]
1953278976 blocks super 1.2 512K chunks 2 far-copies [2/2] [UU]
bitmap: 0/15 pages [0KB], 65536KB chunk

And sudo mdadm --detail /dev/md127 returns:

dev/md127:
Version : 1.2
Creation Time : Sat Nov 27 23:26:46 2021
Raid Level : raid10
Array Size : 1953278976 (1862.79 GiB 2000.16 GB)
Used Dev Size : 1953278976 (1862.79 GiB 2000.16 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent

 Intent Bitmap : Internal

   Update Time : Tue Nov 30 23:22:19 2021
         State : clean 
Active Devices : 2

Working Devices : 2
Failed Devices : 0
Spare Devices : 0

        Layout : far=2
    Chunk Size : 512K

Consistency Policy : bitmap

          Name : feynman:media1  (local to host feynman)
          UUID : fdbab225:d014b874:8d0a50de:b9c94b2b
        Events : 32799

Number   Major   Minor   RaidDevice State
   0       8       17        0      active sync   /dev/sdb1
   1       8        1        1      active sync   /dev/sda1

The bottom line is that everything is the way it should be?!

Best regards,
Fabius

6