RAID Mirrorring with MDADM

So I posted about my RAID solution plenty of times, but I have some additional information.

So here're my current harddrives:

# lsscsi
[0:0:0:0]    disk    ATA      Samsung SSD 860  1B6Q  /dev/sda 
[4:0:0:0]    disk    ATA      WDC WD4003FZEX-0 1A01  /dev/sdb 
[5:0:0:0]    disk    ATA      WDC WD5000AAKS-0 3B01  /dev/sdc 
[5:0:1:0]    disk    ATA      ST2000DM001-1CH1 CC29  /dev/sdd 
[10:0:0:0]   disk    WD       Ext HDD 1021     2021  /dev/sde 
[11:0:0:0]   disk    WD       Ext HDD 1021     2021  /dev/sdf 

Three harddrives of which I use for my RAID 1. One internal SATA drive and two external USB drives.

/dev/sdd - harddrive 2 TB
./dev/sdd1        2048 3907024895 3907022848  1.8T fd Linux raid autodetect

/dev/sde - external WD harddrive 2 TB
/dev/sde1        2048 3907024895 3907022848  1.8T fd Linux raid autodetect

/dev/sdf - external WD harddrive 2 TB
/dev/sdf1        2048 3907024895 3907022848  1.8T fd Linux raid autodetect

And then I had a problem.

# mdadm --detail /dev/md127
/dev/md127:
           Version : 1.2
     Creation Time : Wed Mar  6 22:16:05 2013
        Raid Level : raid1
        Array Size : 1953380160 (1862.89 GiB 2000.26 GB)
     Used Dev Size : 1953380160 (1862.89 GiB 2000.26 GB)
      Raid Devices : 3
     Total Devices : 2
       Persistence : Superblock is persistent

       Update Time : Sat Nov 27 20:57:13 2021
             State : clean, degraded 
    Active Devices : 2
   Working Devices : 2
    Failed Devices : 0
     Spare Devices : 0

Consistency Policy : resync

              Name : micemouse:0
              UUID : ed4531c4:59c132b2:a6bfc3d1:6da3b928
            Events : 6205

    Number   Major   Minor   RaidDevice State
       2       8       65        0      active sync   /dev/sde1
       -       0        0        1      removed
       3       8       49        2      active sync   /dev/sdd1

For some reason, we're missing /dev/sdf with partition /dev/sdf1.

I am fairly concerned here.

So I reattached the device, and then had to rebuild, etc, etc and it took a few days.

mdadm /dev/md127 -a /dev/sdf1

A better solution would have been to prevent the automounting of raid arrays, until I've attached said external drives.

They are not attached by default.

Turning off auto raid detection

The reason I wanted to turn off automatic raid detection, is because I have two disks that can be attached via USB that are part of the RAID array.

When they are not attached, and the raid is autodetected, this time it started up with one device removed.

And it takes a dickens of a time to reattach the devices to the raid.

Sometimes the configuration is simply not there (autodetects the superblock on drives, and works it out from there).

If it is there, it should be either in:

/etc/mdadm/mdadm.conf

for some Linux, for example Ubuntu.

/etc/mdadm.conf

for some Linux, for example Fedora.

Simply adding the following should be enough:

echo "AUTO -all" >> /etc/mdadm.conf

A better way would probably be to have stopped the raid, and re-assemble it again.

Will try this next time if it happens.

Stopping an array

sudo umount /mnt/md127
sudo mdadm --stop --scan

Starting an Array

For simple setups:

sudo mdadm --assemble --scan

For specific setups:

sudo mdadm --assemble /dev/md127 /dev/sdd /dev/sde /dev/sdf

For machine/harddrive independent setup (he gathers the appropriate components itself):

mdadm --scan --assemble --uuid=a26bf396:31389f83:0df1722d:f404fe4c

And then you can do:

sudo mount /dev/md127 /mnt/raid

References

DigitalOcean - How To Manage RAID Arrays with mdadm on Ubuntu 16.04

https://www.digitalocean.com/community/tutorials/how-to-manage-raid-arrays-with-mdadm-on-ubuntu-16-04

Re: turn off auto assembly

https://www.spinics.net/lists/raid/msg30997.html