How to Use the Command 'pvscan' (with Examples)

The pvscan command is a crucial utility in the Linux Logical Volume Manager (LVM) system, used for scanning all physical volumes and managing their online status. By understanding and utilizing pvscan, system administrators can efficiently manage storage devices, monitor their usage, and make informed decisions about storage configurations. For those looking to delve deeper, a full manual is available at manned.org/pvscan .

Use Case 1: List All Physical Volumes

Code:

pvscan

Motivation:

Listing all physical volumes is the fundamental step in managing storage devices, allowing you to identify all available volumes on the system. This is particularly important when you are setting up a new server, performing system audits, or troubleshooting disk space issues. Knowing the physical volumes available can assist in planning volume group allocations and ensure data redundancy and optimal storage utilization.

Explanation:

• pvscan: This command alone is used here, without additional arguments, which triggers a scan of all disks to list all the physical volumes recognized by the LVM system.

Example Output:

  PV /dev/sda1   VG vg0   lvm2 [40.00 GiB / 0  free]
  PV /dev/sdb1   VG vg1   lvm2 [50.00 GiB / 20.00 GiB free]
  Total: 2 [90.00 GiB] / in use: 2 [90.00 GiB] / in no VG: 0 [0   ]

Use Case 2: Show the Volume Group that Uses a Specific Physical Volume

Code:

pvscan --cache --listvg /dev/sdX

Motivation:

Understanding which volume group (VG) a specific physical volume (PV) belongs to can be crucial during storage planning and when performing maintenance or upgrades. This information helps to prevent accidental data loss by ensuring that all components of a volume group are accounted for before any disk operations are carried out. It is also valuable in environments where multiple volume groups might be spread across various physical devices.

Explanation:

• --cache: This option is used to populate the internal cache with current metadata. Keeping cached data helps improve performance in environments with large numbers of devices.
• --listvg: Using this option instructs pvscan to display the name of the volume group that uses a specific physical volume.
• /dev/sdX: This is a placeholder for the physical volume device file you are querying. Replace ‘sdX’ with the actual device name like ‘sda1’, ‘sdb1’, etc.

Example Output:

  PV /dev/sdX   VG vg0

Use Case 3: Show Logical Volumes that Use a Specific Physical Volume

Code:

pvscan --cache --listlvs /dev/sdX

Motivation:

Administrators might need to determine which logical volumes (LVs) are currently using a certain physical volume for better resource allocation and troubleshooting. For instance, if you’re planning to reallocate physical resources, migrating logical volumes without disruption necessitates knowing their exact locations and relationships with physical volumes.

Explanation:

• --cache: Ensures that the latest metadata information is cached for accurate results.
• --listlvs: This argument is used to list all logical volumes that reside on the specified physical volume.
• /dev/sdX: The device name of the physical volume you are investigating.

Example Output:

  LV lv_home   VG vg0   PV /dev/sdX
  LV lv_data   VG vg0   PV /dev/sdX

Use Case 4: Display Detailed Information in JSON Format

Code:

pvscan --reportformat json

Motivation:

In today’s interconnected systems, integrating tools and automating workflows is key. Outputting information in JSON format allows pvscan data to be easily consumed by other programs or scripts, facilitating integration into monitoring dashboards, reporting tools, and automation pipelines. JSON is a lightweight, text-based format that is easy to read and manipulate programmatically.

Explanation:

• --reportformat json: This option changes the output format of the command to JSON, making it suitable for scripts or applications that can process JSON data.

Example Output:

{
  "report": [
    {
      "pv": [
        {"pv_name": "/dev/sda1", "vg_name": "vg0", "pv_size": "40.00g", "pv_free": "0"}
      ]
    }
  ]
}

Conclusion:

Understanding and utilizing the pvscan command is invaluable for anyone managing Linux systems utilizing LVM for flexible and efficient storage management. Whether you need to list all physical volumes, view group associations, track detailed metadata, or automate processes with JSON output, pvscan provides the functionalities to do so effectively. These use cases demonstrate the command’s versatility and importance in maintaining a robust and reliable storage infrastructure.