Provided by: lvm10_1.0.8-8_i386 bug

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  volume  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 logical
       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 volumes
       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.  Physical
       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/VolumeGroupName/ in turn holds a  file  group  containing
       summary      information     for     the     VG     as     a     total.
       /proc/lvm/VGs/VolumeGroupName/LVs/LogicalVolumeName  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>