File System

Mounting File Systems

• Usually you don't need to add lines for disks into /etc/fstab

• The OS will detect and mount the drives automatically, or let the user mount them

• You only need to try adding lines to /etc/fstab if the OS doesn't see the drive at all, but it does show up in "lsblk"

• BE CAREFUL - if you add a line to /etc/fstab and then change the disk partitioning or structure in any way, the system will not be able to mount it on startup and Linux could fail to boot.

  • In my case, I created a hardware RAID after adding the individual HDD's as separate lines to /etc/fstab, causing Ubuntu not to boot (or boot into emergency mode)

  • You might see a message "booting into emergency mode" when it fails to boot.

• The solution is to delete any lines you added from /etc/fstab and it should boot again.

RAID

• UBUNTU DOES NOT LIKE RAID ARRAYS CREATED BY THE INTEL HARDWARE RAID BOARD

  • Intel RST (Rapid Storage Technology) - hardware RAID driver

  • This is strange because I booted from a Lubuntu live USB and it saw the hardware RAID just fine

  • But for whatever reason, Ubuntu 22.04 didn't see the original hardware RAID that was there, and I can't get it to see a new one that I reformat and set up with the Intel hardware.

  • Creating the Intel hardware RAID causes corruption in the first HDD's backup GPT table, which throws a warning in "sudo fdisk -l"

  • When trying to add the hardware RAID into /etc/fstab and mounting it, it throws errors "wrong fs type, bad option, bad superblock, missing codepage or helper program, or other error." Or, "can't read superblock on /dev/…"

  • Clearly the hardware RAID board is modifying the first HDD's partition table in a way that Ubuntu doesn't like.

• Rather than use the hardware RAID, better to use mdadm to make a Linux software RAID.

• sudo apt install mdadm

• man mdadm

• Mdadm cheat sheet | Mdadm Cheat Sheet

• Intel RST in Linux Guide | Intel® Rapid Storage Technology (Intel® RST) in Linux*

  • Contains error in RAID container create command - list of devices must come immediately after "-n 3" option

  • There are numerous errors in the code snippets in this document

• mdadm guide | How to Set Up RAID in Linux

• RAID comparison table | RAID level comparison table

Create RAID Array Using 'mdadm'

1. Create RAID Container

2. Create RAID Volume

3. Create 'mdadm.conf' File

# By default, root doesn't have a password in Ubuntu. Set one as follows.
sudo passwd root
# Must be root for this command - sudo is insufficient
su
mdadm --detail --scan >> /etc/mdadm/mdadm.conf

# Remove this line if it is in the file
name=[devicename]:[x]  # Line format
name=ubuntu-test:0     # Line example

4. Update 'mdadm' to use 'mdadm.conf' File

# Update mdadm to use new mdadm.conf file.
sudo update-initramfs -u

5. Create a Mount Point for the RAID Array and Save it in the '/etc/fstab' File

# Open fstab file.
sudo vim /etc/fstab
# Add the following line (example):
/dev/md0 [path_to_mount_point] ext4 defaults 1 2
# More example fstab file contents for regular individual drives:
/dev/sda1 /media/1TB_CH0 exfat defaults 1 2
/dev/sdb1 /media/1TB_CH1 exfat defaults 1 2

6. Update Permissions to be able to read and write from the RAID drive

# These are recommended but don't always work:
sudo chown [user] [mount path]
sudo chown oakdell /media/oakdell/nas

Great article | fstab mount options for umask, fmask, dmask for ntfs with noexec

List of options for fstab entries | Fstab File ( /etc/fstab ) Entry Options in Linux

# Add these options to /etc/fstab.
# There is no group "users" in Ubuntu by default,
# but one could be created for this purpose.
/dev/md0 /media/username/nas exfat defaults,uid=oakdell,gid=users,dmask=0007,fmask-0117 1 2

# These options also work (if current user is member of group,
# don't need uid). However, for some reason this results
# in deleted files not going to the trash, but being
# permanently deleted with a warning.
/dev/md0 /media/oakdell/nas exfat defaults,gid=oakdell,dmask=0007,fmask-0117 1 2

Get Information About RAID Array

# Display information about the RAID metadata
# format used by mdadm on the current system platform.
mdadm -–detail-platform
# Display RAID metadata format for a specific RAID array.
mdadm --detail /dev/md0

Meaning of "major" and "minor" | https://www.linuxquestions.org/questions/linux-general-1/detailed-information-about-mdadm-output-781033/

# Get RAID config information for a single disk in the array.
sudo mdadm -E /dev/sda
# See which RAID arrays are currently running.
cat /proc/mdstat
# Show real-time updates of the mdstat file to track progress.
watch -d cat /proc/mdstat

Remove RAIDs that were Previously Created

Guide | Removal of mdadm RAID Devices – How to do it quickly?

cat /proc/mdstat
# Do this for each one listed
sudo mdadm --stop /dev/md126
# Do this for each one listed
sudo mdadm --remove /dev/md1

sudo mdadm --zero-superblock /dev/sda /dev/sdb
lsblk
cat /proc/mdstat

Restart a RAID that was Previously Running

sudo mdadm --assembly /dev/md0