LVM(8)							      System Manager's Manual							    LVM(8)

NAME

       lvm - Linux Logical Volume Manager

DESCRIPTION

       lvm is a logical volume manager for Linux.  It enables you to concatenate several physical volumes (hard disks etc.)  into a so called vol-
       ume group (VG, see pvcreate(8) and vgcreate(8) ) forming a storage pool, like a virtual disk.  IDE, SCSI disks as well as multiple  devices
       (MD)  are  supported.   The storage capacity of a volume group can be divided into logical volumes (LVs), like virtual disk partitions. The
       size of a logical volume is in multiples of physical extents (PEs, see lvcreate(8) ).
       The size of the physical extents can be configured at volume group creation time. If a logical volume is too small or  too  large  you  can
       change  its  size  at runtime ( see lvextend(8) and lvreduce(8) ).  lvcreate(8) can be used to create snapshots of existing logical volumes
       (so called original logical volumes in this context) as well.
       Creating a snapshot logical volumes grants access to the contents of the original logical volume it is associated with and exposes the read
       only contents at the creation time of the snapshot. This is useful for backups or for keeping several versions of filesystems online.
       If  you	run  out of space in a volume group it is possible to add one or more pvcreate'd disks to the system and put them into an existing
       volume group ( see vgextend(8) ). The space on these new physical volumes can be dynamically added to logical volumes in that volume  group
       ( see lvextend(8) ).
       To  remove  a physical volume from the system you can move allocated logical extents to different physical volumes ( see pvmove(8) ). After
       the pvmove the volume group can be reduced with the vgreduce(8) command.
       Inactive volume groups must be activated with vgchange(8) before use.  vgcreate(8) automatically activates a newly created volume group.

Abbreviations
       PV for physical volume, PE for physical extent, VG for volume group, LV for logical volume, and LE for logical extent.

Command naming convention
       All command names corresponding to physical volumes start with pv, all the ones concerned with volume groups start with vg and all for log-
       ical volumes with lv.  General purpose commands for the lvm as a whole start with lvm.

VGDA

       The  volume  group  descriptor  area  (or VGDA for short) holds the necessary metadata to handle the LVM functionality. It is stored at the
       beginning of each pvcreate'd disk.  It contains four parts: one PV descriptor, one  VG  descriptor,  the  LV  descriptors  and  several	PE
       descriptors.  LE  descriptors  are  derived  from  the  PE  ones  at vgchange(8) time. Automatic backups of the VGDA are stored in files in
       /etc/lvmconf/ (please see vgcfgbackup(8)/vgcfgrestore(8) too). Take care to include these files in your regular (tape) backups as well.

Limits
       Currently up to 99 volume groups with a grand total of 256 logical volumes can be created. The limit for the logical volumes is not  caused
       by the LVM but by Linux 8 bit device minor numbers.

       This means that you can have 99 volume groups with 1-3 logical volumes each or on the other hand 1 volume group with up to 256 logical vol-
       umes or anything in between these extreme examples.

       Depending on the physical extent size specified at volume group creation time (see vgcreate(8) ), logical volumes of between a  maximum	of
       512  Megabytes  and  1 Petabyte can be created.	Actual Linux kernels on IA32 limit these lvm possibilities to a maximum of 2 Terabytes per
       logical and per physical volume as well. This enables you to have as much as 256 Terabytes under LVM control with  all  possible  128  scsi
       disk subsystems.  You can have up to 65534 logical extents (on IA32) in a logical volume at the cost of 1 Megabyte in kernel memory.  Phys-
       ical volumes can have up to 65534 physical extents.

/proc filesystem support
       The operational state of active volume groups with  their  physical  and  logical  volumes  can	be  found  in  the  /proc/lvm/	directory.
       /proc/lvm/global  contains  a summary of all available information regarding all VGs, LVs and PVs.  The two flags for PV status in brackets
       mean A/I for active/inactive and A/N for allocatable or	non-allocatable.   The	four  flags  for  LV  status  in  brackets  mean  A/I  for
       active/inactive,  R/W  for read-only or read/write, D/C for discontiguous or contiguous and L/S for linear or striped.  S can optionally be
       followed by the number of stripes in the set.  At /proc/lvm/VGs/ starts a subdirectory hierarchy containing information about every VG in a
       different  subdirectory	named  /proc/lvm/VGs/VolumeGroupName  where  VolumeGroupName  stands for an arbitrary VG name.	/proc/lvm/VGs/Vol-
       umeGroupName/ in turn holds a file group containing summary information for the VG  as  a  total.   /proc/lvm/VGs/VolumeGroupName/LVs/Logi-
       calVolumeName  holds  information for an arbitrary LV named LogicalVolumeName /proc/lvm/VGs/VolumeGroupName/PVs/PhysicalVolumeName contains
       information for an arbitrary PV named PhysicalVolumeName.  All of the information  in  the  files  below  /proc/lvm/VGs/  is  presented	in
       attribute/value pairs to be easyly parsable.

Examples
       We have disk partitions /dev/sda3, /dev/sdb1 and /dev/hda2 free for use and want to create a volume group named "test_vg".  Steps required:

       1. Change partition type for these 3 partitions to 0x8e with fdisk.  (see pvcreate(8): 0x8e identifies LVM partitions)

       2. pvcreate /dev/sda3 /dev/sdb1 /dev/hda2

       3. vgcreate test_vg /dev/sda3 /dev/sdb1 /dev/hda2

       With  our  volume group "test_vg" now online, we can create logical volumes. For example a logical volume with a size of 100MB and standard
       name (/dev/test_vg/lvol1) and another one named "my_test_lv" with size 200MB striped (RAID0) across all the three physical volumes.

       Steps required:

       1. lvcreate -L 100 test_vg

       2. lvcreate -L 200 -n my_test_lv -i 3 test_vg

       Now let's rock and roll.  For example create a  file  system  with  "mkfs  -t  ext2  /dev/test_vg/my_test_lv"  and  mount  it  with  "mount
       /dev/test_vg/my_test_lv /usr1"

See also
       e2fsadm(8), lvchange(8), lvcreate(8), lvdisplay(8),
       lvextend(8), lvmchange(8), lvmdiskscan(8),
       lvmcreate_initrd(8), lvmsadc(8), lvmsar(8),
       lvreduce(8), lvremove(8), lvrename(8),
       lvscan(8), pvchange(8), pvcreate(8), pvdata(8),
       pvdisplay(8), pvmove(8), pvscan(8), vgcfgbackup(8),
       vgcfgrestore(8), vgchange(8), vgck(8), vgcreate(8),
       vgdisplay(8), vgexport(8), vgextend(8), vgimport(8),
       vgmerge(8), vgmknodes(8), vgreduce(8), vgremove(8),
       vgrename(8), vgscan(8), vgsplit(8)

AUTHOR

       Heinz Mauelshagen <Linux-LVM@Sistina.com>

Heinz Mauelshagen						     LVM TOOLS								    LVM(8)