LVM (Logical Volume Manager)

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LVM, or Logical Volume Manager, is a tool used on Linux systems to manage disk space in a more flexible way compared to traditional partitioning. It acts like a layer of abstraction between your physical disks and the logical volumes you use for your filesystems. Here's a breakdown of how it works:

Components of LVM:

• Physical Volumes (PV): These are your actual physical hard drives or partitions on those drives. They are the raw storage devices that LVM uses.
• Volume Group (VG): A VG is a collection of PVs that are grouped together under LVM management. You can think of it as a pool of storage space.
• Logical Volume (LV): This is the virtual partition that you create from the storage space in a VG. You can format an LV with a filesystem (like ext4) and use it to store your data just like a regular partition.

Physical Volume (PV) Management:

Initializes a physical disk or partition for use with LVM.

Replace /dev/sdX with the actual device name.

pvcreate /dev/sdX

Displays information about all the PVs in your system.

pvdisplay

Move extents (data chunks) from one PV to another.

This is useful for migrating data or rebalancing PVs within a VG.

pvmove /dev/sdX /dev/sdY

Resizes a physical disk or partition that's already a PV.

pvresize /dev/sdX

pvremove /dev/sdX: Removes a PV from LVM management.

Volume Group (VG) Management:

• vgcreate vg_name /dev/sdX /dev/sdY: Creates a new volume group named vg_name using the specified PVs (/dev/sdX and /dev/sdY). You can add more PVs to a VG later.
• vgdisplay: Displays information about all the VGs in your system.
• vgreduce vg_name /dev/sdX: Removes a PV from a volume group (assuming there are other PVs in the VG and the data is not exclusively on the PV being removed).
• vgremove vg_name: Removes a volume group entirely. This destroys the VG and all its LVs. Use with caution!

Logical Volume (LV) Management:

• lvcreate -n lv_name -L <size> vg_name: Creates a new logical volume named lv_name with the specified size <size> within the volume group vg_name. You can specify the size in various units (e.g., M for Megabytes, G for Gigabytes).
• lvdisplay: Displays information about all the LVs in your system.
• lvextend -L <size> /dev/mapper/vg_name-lv_name: Extends the size of an existing LV. Replace <size> with the desired expansion size.
• lvreduce -L <size> /dev/mapper/vg_name-lv_name: Reduces the size of an existing LV. Use with caution as data loss might occur if shrinking beyond the size of the data written on the LV.
• lvremove /dev/mapper/vg_name-lv_name: Removes a logical volume from the VG. The space becomes available for other LVs within the VG.
• lvresize [OPTIONS] LV [PV ...]: Resizes an existing LV. This command was covered in detail previously.

Information and Scanning:

• lvmconfig: Displays global LVM configuration information.
• vgscan: Scans all disks for PVs. This updates LVM's internal information about available physical devices.
• lvscan: Scans all VGs for LVs. This updates LVM's information about logical volumes within existing VGs.