HP Logical Volume Manager (LVM)

HP Logical Volume Manager (LVM)

Logical Volume Manager is a disk management subsystem that allows you to manage physical disks as logical volumes.

The following terms are used when working with LVM:

Volume	A volume is a device used for a filesystem, swap or raw data. Without LVM a volume would be a disk partition or the whole disk
Physical Volume	A physical volume is the disk itself. An entire disk must be initialised if it is to be used by LVM.
Volume Group	A volume Group is a collection of volumes that are managaed by LVM. Each disk must only belong to one group however a volume group many contain many disks.
Logical Volume	This is the space that is defined within a volume group. The volume group is divided into smaller logical volumes which in turn become the filesystems. A volume group may contain one or many logical volumes. Logical volumes can be grown or shrunk. A logical volume is a set of logical extents
Physical Extent	A physical extent is a set of contiguous disk blocks on a physical volume. The default size of an extent is 4MB but this can be adjusted when initialising the disk. Normally a physical extent will have a one to one relationship with logical extents.
Logical Extent	A logical volume is a set of logical extents. Logical extents and pyhsical extents are the same size in a volume. A logical extent is a direct mapping to a pyhsical extent.
/etc/lvmtab	This file has in it the device file associated with each disk in a volume group. /sbin/lvmrc starts each volume group by reading the contents of this file at boot time.This file can be rebuilt using the command vgscan. The file is a binary file and can be read using Strings.
PV Links	Physical Volume Links (PV Links) provide dual SCSI or FL links to the same disk. This basically means multipathing to a disk.

Boot Disk Components

LIF Directory* Contains a list of other disks in the volume group and whether or not they are bootable PVRA Contains imports PV-related information such as: PV ID number VG ID number PE Size PV size bad block directory This is created when pcreate is run BDRA* Specifies where the root filesystem is found LIF* Contains ISL, HPUX, AUTO, LABEL that are LIF files. These are put there when the mkboot and lvlnboot commands are run. VGRA Contain volume group description area (VGDA) and volume group status area (VGSA) Physical Extents Physical extents for the file system, swap, etc Bad Block Pool Provides alternate locations for bad blocks * Boot disk Only

Disk Mirroring

Disk Mirroring is preformed by the sftware package MirrorDisk/UK, the product requires a license from HP. Logical volumes can be mirror one or more times, in other words the logical extent is mapped to one or more physical extents. There is a mirror policy called strict which can be set to one of the following:

n	when set means that mirrored copies of a logical extent can share the same physical volume. This means that your original and mirrored data may be on the same physical disk
y	when set means that mirrored copies of a logical extent cannot share the same physical volume. This means that your original and mirrored data will not share the physical disk
g	Mirrored data will not be on the same physical volume group (PVG) as the original data. This policay is called a PVG-strict allocation policy.

Physical Volume Commands

pvchange	Allows you to change a physical volume is some way. for an example you can allow or disallow adding extents to this physical volume.
pvcreate	Is used to create a physical volume that will be part of a volume group.
pvdisplay	shows information about a physical volumes you specify
pvmove	you can move extents from one physical volume to other physical volumes.
mknod	this command is used to create th major/minors numbers of a volume group

Volume Group Commands

vgcfgbackup	used to save the configuration of a volume group.
vgcfgrestore	used to restore the configuration of a volume group.
vgchange	makes a volume active or in-active
vgcreate	you can create a volume group and specify all of its parameters.
vgdisplay	display information related to a volume group
vgexport	remove a volume group from the system, but does not modify the logical volume information on the physical volumes. You can then import the volume group onto another system i.e in a cluster environment.
vgextend	Physical volumes can be added to a volume group by specifying the physical volume to be added to the volume group.
vgimport	used to import a volume group from another system
vgreduce	reduce the volume group by removing th specified physical volume.
vgremove	remove the volume group completely from the system
vgscan	rebuild the /etc/lvmtab file
vgsync	when a volume group become stale you can resync that volume which resync's all the physical extents in each mirrored logical volume in the volume group.

Logical Volume Commands

lvcreate	create a new logical volume.
lvchange	change the logical volume in some way
lvdisplay	display information on a specified logical volume
lvextend	increase the number of physical extents to a logical volume. You will need to use the extendfs after extending a logical volume.
extendfs	expands the filesystem within the logical volume. You would use fsadm if you have OnlineJFS installed.
mkboot	places boot utilities in boot area
lvlnboot	use this to sepup a logical volume to be a root, boot, primary swap or dump volume. This can be undo with lvrmboot.
lvsplit or lvmerge	are used to split or merge a logical volume that is mirrored
lvmmigrate	prepares a root filesystem in a disk partition for migration to a logical volume. You would use this if you had a partition to convert to a logical volume
lvreduce	decrease the number of physical extents allocated to a logical volume
lvremove	remove a logical volume from the volume group
lvrmboot	if you don't want a logical volume to be root, boot, primary swap or a dump device.
lvsync	when a logical volume becomes stale you can resync the logical volume
newfs	place a new flesystem on a logical volume

JFS and OnlineJFS Commands

fsck	check/repair the integrity of a filesystem
fsadm	peforms a number of tasks when using a OnlineJFS sch as dfragmentation, resizing, online backup, etc

Commonly used LVM procedures

Create a new volume group, logical volume and filesystem	pvcreate /dev/rdsk/c0t1d0 mkdir /dev/vg01 mknod /dev/vg01/group c 64 0x010000 vgcreate /dev/vg01 /dev/dsk/c0t1d0 lvcreate -L 2000 /dev/vg01 newfs -F vxfs -o largefiles /dev/vg01/rlvol1 mkdir /ora_data01 mount /dev/vg01/lvol1 /ora_data01
Create a stripped filesystem	lvcreate -i 3 -I 32 -L 24 -n lvol1 /dev/vg01 -i number of stripes -I stripe size of 32KB -L size of the volume
Mirror root and swap disk	pvcreate -B /dev/rdsk/c0t6d0 vgextend /dev/vg00 /dev/dsk/c0t6d0 mkboot /dev/rdsk/c0t6d0 mkboot -a "hpux -lq" /dev/rdsk/c0t6d0 mkboot -a "hpux -lq" /dev/rdsk/<primary disk> lvextend -m 1 /dev/vg00/lvol1 /dev/dsk/c0t6d0 lvextend -m 1 /dev/vg00/lvol2 /dev/dsk/c0t6d0 lvextend -m 1 /dev/vg00/lvol3 /dev/dsk/c0t6d0 lvextend ........all other volumes on primary disk setboot -a 8/8.6.0
replace a non-mirrored disk	lvreduce -m 0 -A n /dev/vg01/lvol1 /dev/dsk/cxtxdx vgreduce vg01 /de/dsk/cxtxdx or pvchange -a N /dev/dsk/cxtxdx (if you have online replacement disks) vgcfgrestore -n /dev/vgXX /dev/rdsk/cxtxdx vgchange -a y /dev/vgXX newfs -F <fstype> /dev/vgXX/rlvolx mount <mountpoint> Notes: Make sure you have /etc/lvmconf/vgXX.conf vgcfgbackup is run automatically Defective disk was not mirrored before it failed
replace a mirrored disk	vgcfgrestore -n /dev/vgXX /dev/rdsk/cxtxdx vgchange -a y /dev/vgXX vgsync /dev/vgXX Notes: Defective disk was mirrored before it failed
replace mirrored boot disk	vgcfgrestore -n /dev/vg00 /dev/rdsk/cxtxdx vgchange -a y /dev/vg00 vgsync /dev/vg00 mkboot /dev/rdsk/cxtxdx mkboot -a "hpux -lq" /dev/rdsk/cxtxdx shutdown -r -y 0 Notes: Confirm that you have /etc/lvmconf/vg00.conf Defective disk was mirrored before it failed
export and import a volume group	System One: vgchange -a n /dev/vg01 vgexport -v -m /tmp/mapfile -s /dev/vg01 rcp /tmp/mapfile <system 2>:/tmp/mapfile System two: mkdir /dev/vg01 mknod /dev/vg01/group c 64 0xyy0000 vgimport -v -m /tmp/mapfile -s /dev/vg01 vgchange -a y /dev/vg01 mkdir /ora_data01 mount /dev/vg01/ora_data01 /ora_data01
extend VxFS file ssytem using onlineJFS	lvextend -L 800 /dev/vg01/lvol1 fsadm -F vxfs -b 800M /ora_data01
change a logical volume to support largefiles	fsadm -F vxfs -o largefiles /dev/vg01/rlvol1
display the boot area	lifls -Clv /dev/dsk/c0t6d0
display boot information	lvlnboot -v /dev/vg00
display all disks in the system	ioscan -funC disk
make a dump device	lvchange -C y /dev/vg00/dump (makes it contiguous) lvlnboot -d /dev/vg00/dump
display dump devices	lvlnboot -v