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. |
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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. |
| 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 |
| 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. |
| 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 |
| 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 |
| 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 |
Courtesy by datadisk.co.uk
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