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LVM(8)											   LVM(8)

       lvm - Linux Logical Volume Manager

       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  vgcre-
       ate(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 lvex-
       tend(8) and lvreduce(8) ).  lvcreate(8) can be used to create snapshots of existing  logi-
       cal 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
       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 dif-
       ferent 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) auto-
       matically activates a newly created volume group.

       PV for physical volume, PE for physical extent, VG for volume group, LV for  logical  vol-
       ume, 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.

       The  volume group descriptor area (or VGDA for short) holds the necessary metadata to han-
       dle the LVM functionality. It is stored at the beginning of each pvcreate'd disk.  It con-
       tains  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)/vgcf-
       grestore(8) too). Take care to include these files in your regular (tape) backups as well.

       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

       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  vgcre-
       ate(8) ), logical volumes of between a maximum of 512 Megabytes and 1 Petabyte can be cre-
       ated.  Actual Linux kernels on IA32 limit these lvm possibilities to a maximum of  2  Ter-
       abytes  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 avail-
       able 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 informa-
       tion  for an arbitrary LV named LogicalVolumeName /proc/lvm/VGs/VolumeGroupName/PVs/Physi-
       calVolumeName 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.

       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)

       Heinz Mauelshagen <Linux-LVM@Sistina.com>

Heinz Mauelshagen			    LVM TOOLS					   LVM(8)
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