L V M A Logical Volume Manager for Linux by Heinz Mauelshagen Sistina, Inc.

Definition of the LVM  the Logical Volume Manager is a subsystem for on-line disk storage management  it adds an additional layer to the i/o subsystem of the kernel to get a virtual view on disks  LVM enables you to deal with »virtual disks« and »virtual partitions« being fully online resizable and movable

LVM Concept1 LVM Concept1  usage of physical disks, disk partitions, multiple or loop devices as PVs (Physical Volumes; basic allocation device)  store metadata in so called VGDAs (Volume Group Descriptor Areas) on the PVs  group PVs in VGs (Volume Groups; »virtual disks«)

LVM Concept2 LVM Concept2  allocate VG storage to LVs (Logical Volumes; »virtual partitions«); basic units called PEs (Physical Extents) are mapped to their LEs (Logical Extents).  extend and reduce VGs and LVs online  use LVs like disks, disk partitions etc. for filesystems, databases etc.  access VGs and LVs via device special files named /dev/VolumeGroupName/*

LVM Concept3  build a command and a library layer to ease the integration of different or additional tools or graphical user interfaces  export and import VGs to bring them to or get them from different computer systems  support linear and striped (RAID0) LVs  support snapshot LVs

Storage Architecture Storage Architecture  2 PVs 2 PVs

Storage Architecture Storage Architecture  VG with 2 PVs VG PVPV

Storage Architecture Storage Architecture  VG with 2 PVs and 1 LV LV VG PVPV

Software Metrics1 Software Metrics1  99 VGs max  256 LVs total (todays 8 bit minor #) in all VGs with ext2 (devfs tents to raise this)  256 PVs total in one VG  up to PEs total per PV  up to LEs per LV  PE/LE sizes between several KB 8*) and GB  cabable of dealing with more than 1000 TB but limited by unsigned long variables in the Linux I/O subsystem on 32 bit platforms (128SCSI Ids*2TB*15 Partitions = 3b840TB)

Upcomming Release + persistent snapshots + resizable snapshots + integration of LVM with the VFS to support atomic snapshot activation (reiserfs) + renaming of Volume Groups and Logical Volumes without deactivating them + devfs support