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Disk Management and LVM

Category: Advanced Linux Administration
Type: Linux Commands
Generated on: 2025-07-10 03:14:07
For: System Administration, Development & Technical Interviews

Disk Management and LVM Cheatsheet (Linux)

Section titled “Disk Management and LVM Cheatsheet (Linux)”

This cheatsheet provides a comprehensive overview of disk management and Logical Volume Management (LVM) commands in Linux, useful for both beginners and experienced system administrators.

1. Command Overview

Section titled “1. Command Overview”
  • Disk Management: Deals with physical disks and partitions. Includes commands for listing, creating, formatting, and mounting partitions.
  • LVM (Logical Volume Management): Provides a layer of abstraction over physical disks, allowing for flexible management of storage space. LVM enables easy resizing, snapshotting, and striping of volumes.

2. Basic Syntax

Section titled “2. Basic Syntax”

Disk Management:

  • fdisk <disk>: Partition table manipulator.
  • parted <disk>: Advanced partition editor.
  • mkfs.<fstype> <device>: Create a filesystem on a partition (e.g., mkfs.ext4 /dev/sda1).
  • mount <device> <mountpoint>: Mount a filesystem.
  • umount <mountpoint>: Unmount a filesystem.
  • df -h: Display disk space usage.
  • du -sh <directory>: Display directory size.
  • lsblk: List block devices.
  • blkid: Display block device attributes (UUID, TYPE).

LVM:

  • pvcreate <device>: Create a Physical Volume (PV).
  • vgcreate <vgname> <pv>: Create a Volume Group (VG).
  • lvcreate -L <size> -n <lvname> <vgname>: Create a Logical Volume (LV).
  • pvdisplay <pv>: Display PV information.
  • vgdisplay <vg>: Display VG information.
  • lvdisplay <lv>: Display LV information.
  • lvextend -L <size> <lv>: Extend an LV.
  • lvreduce -L <size> <lv>: Reduce an LV (requires filesystem resize).
  • lvremove <lv>: Remove an LV.
  • vgremove <vg>: Remove a VG.
  • pvremove <pv>: Remove a PV.
  • vgs: Summary of Volume Groups.
  • lvs: Summary of Logical Volumes.
  • pvs: Summary of Physical Volumes.
  • lvresize: Resize a logical volume (requires filesystem resize).
  • vgextend: Add a physical volume to a volume group.
  • vgreduce: Remove a physical volume from a volume group.

3. Practical Examples

Section titled “3. Practical Examples”

Disk Management:

  • List block devices:

    Terminal window
    lsblk
    NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
    sda      8:0    0   20G  0 disk
    ├─sda1   8:1    0   500M  0 part /boot/efi
    ├─sda2   8:2    0     1G  0 part /boot
    └─sda3   8:3    0  18.5G  0 part
      └─vg0-root 253:0    0  18.5G  0 lvm  /
    sdb      8:16   0   10G  0 disk
    sdc      8:32   0   10G  0 disk

  • Create a partition table (GPT) on /dev/sdb:

    Terminal window
    parted /dev/sdb mklabel gpt

  • Create a new partition using parted (1GB, starting at 1MB):

    Terminal window
    parted /dev/sdb mkpart primary ext4 1MB 1025MB

  • Format the partition /dev/sdb1 with ext4:

    Terminal window
    mkfs.ext4 /dev/sdb1

  • Mount the partition /dev/sdb1 to /mnt/data:

    Terminal window
    mkdir -p /mnt/data
    mount /dev/sdb1 /mnt/data

  • Add an entry to /etc/fstab for persistent mounting:

    Terminal window
    echo "/dev/sdb1 /mnt/data ext4 defaults 0 0" | sudo tee -a /etc/fstab

  • Unmount /mnt/data:

    Terminal window
    umount /mnt/data

LVM:

  • Create Physical Volumes (PVs) on /dev/sdb and /dev/sdc:

    Terminal window
    pvcreate /dev/sdb
    pvcreate /dev/sdc
    Physical volume "/dev/sdb" successfully created.
    Physical volume "/dev/sdc" successfully created.

  • Create a Volume Group (VG) named data_vg:

    Terminal window
    vgcreate data_vg /dev/sdb /dev/sdc
    Volume group "data_vg" successfully created

  • Create a Logical Volume (LV) named data_lv of size 8GB:

    Terminal window
    lvcreate -L 8G -n data_lv data_vg
    Logical volume "data_lv" created.

  • Format the LV /dev/data_vg/data_lv with ext4:

    Terminal window
    mkfs.ext4 /dev/data_vg/data_lv

  • Mount the LV /dev/data_vg/data_lv to /mnt/data:

    Terminal window
    mkdir -p /mnt/data
    mount /dev/data_vg/data_lv /mnt/data

  • Extend the LV data_lv by 2GB:

    Terminal window
    lvextend -L +2G /dev/data_vg/data_lv
    resize2fs /dev/data_vg/data_lv  # Resize the filesystem

  • Reduce the LV data_lv by 1GB (WARNING: DATA LOSS POSSIBLE! BACKUP FIRST!)

    Terminal window
    umount /mnt/data  # Unmount the LV before reducing
    e2fsck -f /dev/data_vg/data_lv # Check for filesystem errors
    resize2fs /dev/data_vg/data_lv 9G # Resize the filesystem to the new size
    lvreduce -L 9G /dev/data_vg/data_lv
    mount /dev/data_vg/data_lv /mnt/data # Remount the LV

  • Remove the LV data_lv:

    Terminal window
    umount /mnt/data
    lvremove /dev/data_vg/data_lv

  • Remove the VG data_vg:

    Terminal window
    vgremove data_vg

  • Remove the PVs /dev/sdb and /dev/sdc:

    Terminal window
    pvremove /dev/sdb
    pvremove /dev/sdc

4. Common Options

Section titled “4. Common Options”

Disk Management:

  • fdisk:
    • n: Create a new partition.
    • d: Delete a partition.
    • p: Print the partition table.
    • w: Write changes to disk. USE WITH CAUTION!
    • q: Quit without saving.
  • mkfs:
    • -t <fstype>: Specify the filesystem type (e.g., ext4, xfs, btrfs).
    • -L <label>: Set the volume label.
  • mount:
    • -t <fstype>: Specify the filesystem type.
    • -o <options>: Mount options (e.g., ro, noatime, defaults).
  • df:
    • -h: Human-readable format.

LVM:

  • lvcreate:
    • -L <size>: Specify the size of the LV (e.g., 10G, 500M).
    • -n <lvname>: Specify the name of the LV.
    • -l <extents>: Specify the size in logical extents (instead of size).
    • -T: Create a thin pool logical volume.
  • lvextend:
    • -L <size>: Specify the new size of the LV. Use + to add to the existing size (e.g., +2G).
    • -r: Resize the filesystem automatically after extending the LV.
  • lvreduce:
    • -L <size>: Specify the new size of the LV. Use - to subtract from the existing size. WARNING: DATA LOSS POSSIBLE!
  • vgcreate:
    • -s <size>: Specify the physical extent size (PE size). Smaller PE sizes allow for finer-grained allocation, but can increase metadata overhead.
  • lvdisplay, vgdisplay, pvdisplay:
    • -v: Verbose output.

5. Advanced Usage

Section titled “5. Advanced Usage”

LVM:

  • Creating Snapshots:

    Terminal window
    lvcreate -s -L 2G -n data_snap -p r /dev/data_vg/data_lv # Create a snapshot
    mount /dev/data_vg/data_snap /mnt/snapshot
    # Make changes to the original volume /dev/data_vg/data_lv
    # To revert to the snapshot: umount /mnt/data; lvconvert --merge /dev/data_vg/data_snap
    • -s: Create a snapshot.
    • -p r: Set read-only permissions on the snapshot.
    • lvconvert --merge: Merge the snapshot back into the original volume. WARNING: This is a destructive operation!

  • Creating Thin Pools and Thin Volumes:

    Terminal window
    lvcreate -L 100G -n thinpool data_vg # Create a thin pool
    lvconvert --thinpool data_vg/thinpool --yes
    lvcreate -T data_vg/thinpool -V 10G -n thinvol1 # Create a thin volume
    lvcreate -T data_vg/thinpool -V 10G -n thinvol2 # Create another thin volume
    

    mkfs.ext4 /dev/data_vg/thinvol1
    mkfs.ext4 /dev/data_vg/thinvol2
    

    mount /dev/data_vg/thinvol1 /mnt/thin1
    mount /dev/data_vg/thinvol2 /mnt/thin2
    • -T: Create a thin pool LV.
    • -V: Virtual size of the thin volume. The actual space used will be less until data is written.
    • Thin pools enable over-provisioning.

  • LVM Striping (Improved Performance):

    Terminal window
    lvcreate -i 2 -I 64 -L 10G -n striped_lv data_vg  # Striped across 2 PVs, 64KB stripe size
    • -i <number>: Number of stripes.
    • -I <size>: Stripe size in KB.

  • Migrating Physical Volumes:

    Terminal window
    pvmove /dev/sdb /dev/sdc  # Move data from /dev/sdb to /dev/sdc
    vgreduce data_vg /dev/sdb # Remove /dev/sdb from the VG after successful migration

  • Activating/Deactivating Volume Groups:

    Terminal window
    vgchange -a y data_vg  # Activate the VG
    vgchange -a n data_vg  # Deactivate the VG
    • -a y: Activate the VG.
    • -a n: Deactivate the VG.

6. Tips & Tricks

Section titled “6. Tips & Tricks”
  • Tab Completion: Use tab completion for device names, VG names, and LV names.
  • watch command: Use watch -n 1 lvs or watch -n 1 pvs to monitor LVM changes in real-time.
  • pvresize: Use pvresize after resizing a partition that contains a PV. This updates the PV’s size to match the partition.
  • Backup: Always back up important data before performing any disk management or LVM operations. Use dd to create disk images, or use LVM snapshots.
  • Filesystem Check: Always run fsck on a filesystem after resizing or if you suspect corruption.
  • LVM Auto-activation: Ensure LVM is configured to automatically activate volume groups on boot. Check /etc/lvm/lvm.conf for the auto_activation setting.
  • Logical Extent Size: The logical extent size is crucial in LVM. Once a VG is created with a specific extent size, it cannot be changed. Smaller extent sizes allow for more granular control but increase metadata overhead.
  • pvs -o +pe_start: View the starting physical extent for each PV within a VG.

7. Troubleshooting

Section titled “7. Troubleshooting”
  • “Device or resource busy”: The device is likely mounted. Unmount it before attempting to modify it.
  • “Invalid argument”: Check the syntax of your command. Double-check device names and sizes.
  • “Volume Group not found”: The VG may not be activated. Use vgchange -a y <vgname>. Also, ensure LVM is properly initialized on boot.
  • “Filesystem needs to be checked”: Run fsck on the filesystem.
  • Data Loss: Always back up your data before resizing, reducing, or removing volumes. Double-check your commands before executing them.
  • LVM Not Activating on Boot:
    • Ensure LVM is enabled in your initramfs.
    • Check /etc/fstab for correct entries.
    • Verify that the lvm2-activation service is running.
  • Stale Physical Volumes: If a PV is no longer available (e.g., disk failure), you may need to use vgreduce --removemissing to remove it from the VG. WARNING: Data loss is possible if the PV contained important data.
Section titled “8. Related Commands”
  • xfs_growfs: Resize an XFS filesystem.
  • resize2fs: Resize an ext2/3/4 filesystem.
  • gdisk: GPT disk partitioner, alternative to fdisk for GPT disks.
  • lvmdiskscan: Scan for LVM physical volumes.
  • pvck, vgck, lvck: LVM consistency check tools.
  • cryptsetup: For encrypting disks and partitions.
  • mdadm: Software RAID management.
  • systemd-mount: Mount filesystems using systemd units.
  • wipefs: Clear filesystem, RAID or partition-table signatures from a device.

This cheatsheet provides a solid foundation for managing disks and LVM in Linux. Remember to always back up your data and carefully review commands before execution, especially when dealing with destructive operations.