Mount Show Unknown Filesystem Type 'lvm2_member'

7 min read Oct 04, 2024

Mount Show Unknown Filesystem Type 'lvm2_member'

Encountering the "mount: unknown filesystem type 'lvm2_member'" Error? Here's What You Need to Know!

Have you stumbled upon the cryptic error message "mount: unknown filesystem type 'lvm2_member'"? This error often crops up when trying to mount a logical volume within a Linux system. While it might seem intimidating, understanding the underlying concepts and troubleshooting steps can help you overcome this challenge.

Let's break down what's happening and how to resolve this "mount: unknown filesystem type 'lvm2_member'" error.

Understanding Logical Volume Management (LVM)

LVM (Logical Volume Management) is a powerful technology in Linux that provides a flexible way to manage storage. It allows you to:

Create flexible volumes: Easily create logical volumes that can span multiple physical disks, enhancing storage capacity.
Resize volumes: Resize logical volumes without needing to reformat partitions, offering greater flexibility in managing disk space.
Mirror and stripe volumes: Increase performance and redundancy by mirroring or striping data across multiple physical disks.

Why "lvm2_member" is Not a Filesystem Type

The error message "mount: unknown filesystem type 'lvm2_member'" arises because 'lvm2_member' is not a traditional filesystem type. Think of it as a "container" or "meta-filesystem" that holds other filesystems, like ext4, XFS, or Btrfs. This container itself isn't designed to be mounted directly.

Troubleshooting Steps

Here's a step-by-step guide to address the "mount: unknown filesystem type 'lvm2_member'" error:

Identify the Logical Volume:
- Use the lvs command to list all available logical volumes. Look for the volume that you're trying to mount.
- Example: lvs might show something like:
```
LV       VG       Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync  Conversion
myvol    myvg      -wi-ao----  10.00G          0.00   0.00   0.00   0.00  
```
- In this case, "myvol" is the logical volume.
Verify the Filesystem Type:
- Use the pvdisplay command to view information about the physical volumes (PVs) underlying your logical volume.
- Locate the PV that contains the logical volume you're trying to mount.
- Within the output of pvdisplay, look for the "fmt" field. This indicates the filesystem type.
- Example:
```
PV: /dev/sdb1
...
Fmt: ext4
```
- Here, the filesystem type is "ext4," which is a typical Linux filesystem.
Mount the Underlying Filesystem:
- Now, you need to mount the underlying filesystem within your logical volume.
- Use the mount command, specifying the correct device and filesystem type.
- Example:
```
sudo mount /dev/myvg/myvol /mnt/myvol -t ext4
```
- Replace /dev/myvg/myvol with the path to your logical volume and /mnt/myvol with the desired mount point. Replace "ext4" with the actual filesystem type found in step 2.

Example Scenario

Let's say you're trying to mount a logical volume named "data" residing in the volume group "vg1," but it's throwing the "mount: unknown filesystem type 'lvm2_member'" error.

Identify the Logical Volume:

lvs might output:

LV       VG       Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync  Conversion
data     vg1      -wi-ao----  50.00G          0.00   0.00   0.00   0.00

Verify the Filesystem Type:
- pvdisplay might show:
```
PV: /dev/sdc1
...
Fmt: xfs
```
- You see the filesystem type is "xfs."
Mount the Underlying Filesystem:
- Use the following command:
```
sudo mount /dev/vg1/data /mnt/data -t xfs
```

Additional Tips

Examine your fstab: Check the /etc/fstab file for any entries related to the logical volume you're trying to mount. Ensure that the correct device, filesystem type, and mount options are specified.
Check for errors: Run dmesg or journalctl to view system logs and potentially identify other errors related to LVM that might be causing the issue.

Conclusion

The "mount: unknown filesystem type 'lvm2_member'" error arises because you're trying to mount a logical volume directly, rather than the underlying filesystem within it. By understanding the nature of LVM and following the provided troubleshooting steps, you can confidently resolve this issue and access your logical volume data. Remember to always verify the filesystem type and mount the appropriate underlying filesystem.