When working with LVM (Logical Volume Manager), you might encounter the frustrating "Device excluded by a filter" error while trying to extend a volume group. This typically occurs when the system's LVM filter configuration prevents access to the specified device.

The most frequent reasons for this issue include:

• LVM filters configured in /etc/lvm/lvm.conf
• Device not properly initialized for LVM use
• Permissions issues on the device
• Device already in use by another system

First, examine your current LVM configuration:

# Check current filter settings
grep filter /etc/lvm/lvm.conf

# Alternative method to view active filters
lvmconfig --type default --withcomments | grep filter

1. Temporarily Override Filters

For testing purposes, you can temporarily override filters:

vgextend --config 'devices { filter = [ "a|.*|" ] }' vg_name /dev/sdb

2. Permanently Modify LVM Configuration

Edit /etc/lvm/lvm.conf and adjust the filter line. A common configuration would be:

filter = [ "a|^/dev/sd.*|", "r|.*|" ]

After making changes, refresh LVM:

pvscan --cache
vgscan --mknodes

3. Verify Device Availability

Before adding to LVM, ensure the device is properly prepared:

# Check if device has existing signatures
pvdisplay /dev/sdb

# Wipe existing signatures if needed
wipefs -a /dev/sdb

If the issue persists, consider these additional checks:

# Check device major:minor numbers
ls -l /dev/sdb

# Verify device is not busy
lsof /dev/sdb

# Check kernel messages
dmesg | grep sdb

Here's a complete example of properly adding a device to a volume group:

# Prepare the physical device
pvcreate /dev/sdb

# Check for filters
grep filter /etc/lvm/lvm.conf

# Temporarily allow all devices if needed
vgextend --config 'devices { filter = [ "a|.*|" ] }' my_vg /dev/sdb

# Verify the extension
vgs
pvs

To avoid similar problems:

• Document your LVM filter configuration
• Test new devices with pvdisplay before adding to VGs
• Consider using device UUIDs instead of paths in filters
• Maintain consistent filter policies across all systems

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When working with LVM (Logical Volume Manager) on Linux systems, you might encounter this frustrating error during volume group extension:

vgextend my_vg /dev/sdb
Device /dev/sdb excluded by a filter

The root cause lies in LVM's device filtering system, which controls what physical devices are visible to LVM operations. By default, LVM scans all available block devices in /dev, but certain filters can exclude specific devices.

First, examine your current filter settings:

cat /etc/lvm/lvm.conf | grep filter

You'll typically see something like:

filter = [ "a|.*/|" ]  # Accept all devices by default
# Or more restrictive filters like:
filter = [ "r|/dev/sd[a-c]|", "a|.*/|" ]

Filters use regular expressions with these prefixes:

• a - accept pattern
• r - reject pattern

Here are three ways to resolve this:

1. Temporary Workaround (Testing)

Override filters temporarily for testing:

lvdisplay --config 'devices { filter = [ "a|.*|" ] }'
vgextend --config 'devices { filter = [ "a|.*|" ] }' my_vg /dev/sdb

2. Permanent Solution

Edit /etc/lvm/lvm.conf:

# Backup first!
cp /etc/lvm/lvm.conf /etc/lvm/lvm.conf.bak

# Then modify the filter line to include your device:
filter = [ "a|/dev/sdb|", "a|/dev/sd[a-z]|", "r|.*|" ]

3. Alternative Approach

If using device mapper paths instead:

ls -l /dev/mapper/
vgextend my_vg /dev/mapper/mpatha

After modifying filters, refresh LVM:

pvscan
vgscan
lvscan

For a system where /dev/sdb is a new SSD, but being filtered out:

# Check if device is visible to LVM:
pvs /dev/sdb

# If filtered, temporarily accept all:
vgextend --config 'devices { filter = [ "a|.*|" ] }' my_vg /dev/sdb

# Then make permanent change to lvm.conf:
filter = [ "a|/dev/sdb|", "a|/dev/sda[0-9]|", "r|.*|" ]

For deeper investigation:

lvmdump -m lvm.log
dmsetup table
lsblk -o NAME,FSTYPE,LABEL,MOUNTPOINT