AIX Logical Volume Manager (LVM)
This is a quick and dirty cheat sheet on LVM using AIX, I have highlighted many of the common attributes for each command however this is not an extensive list, make sure you look up the command.
First a quick review on some of the terminology that AIX LVM uses
| Examples | What it means |
| PHYSICAL VOLUME (PV) | Represents a hard disk (hdisk0). |
| PHYSICAL PARTITION (PP) | The smallest allocation unit in the LVM. All PPs within a VG are the same size, usually 4 or 8 MB. |
| VOLUME GROUP (VG) | A set of one or more PVs which form a single storage pool. You can define multiple VGs on each AIX system. |
| LOGICAL VOLUME (LV) | One or more PPs. A file system resides on top of an LV. Only one LV is mapped to a file system. A LV can't span across a VG. Up to 255 LVs in a VG |
| LOGICAL PARITITION (LP) | One or more PPs. LP represents a mirrored copy of a PP. Up to two copies of a PP can be mirrored resulting in a LP count of three (2 mirrors plus original). |
Volume Group Descriptor Area (VGDA) | Information about all the LVs and PVs within a VG. The first 64K of a PV is reserved for this area - defined in <sys/bootrecord.h>. The VGDA consists of
|
Volume Group Status Area (VGSA) | Information about which PPs that are stale and which PVs are missing within a VG. The LVM and SCSI driver reserves somewhere between 7-10% of the available disk space for LVM maps, etc. |
| Physical Volume ID (PVID) | The PVID is an amalgamation of the machine’s serial number (from the systems EPROMs) and the date that the PVID is being generated. This combination insures theextremely low chance of two disks being created with the same PVID. Finally, when a system is booted, the disk configurator goes and looks at the PVID sitting on each disk platter and then compares that to an entry in ODM. If the entry is found, then the disk is given the hdiskX name that is associated with the ODM entry for the PVID. |
| Quorum | Quorum is a sort of “sanity” check that LVM uses to resolve possible data confliction and prevent data corruption. Quorum is a method by which 51% or more quorum votes must be available to a volume group before LVM actions can continue. Quorum is issued to a disk in a volume group according to how the disk was created within the volume group. When a volume group consists of one disk, there are two VGDA’s on that disk. Thus, this single disk volume group has a quorum vote of 2. When another disk is added to the volume group with an “extendvg”, then this new disk gets one VGDA, but the original, first disk still retains the two VGDA’s. When the volume group has been extended to three disks, the third disk gets the spare VGDA sitting on the first disk and then each disk has a quorum vote of 1. Every disk after the third disk is automatically given one VGDA, and thus one vote. |
| Volume Group ID (VGID) | Just as the PVID is a soft serial number for a disk, the VGID is the soft serial number for the volume group. It is this serial number, not the volume group’s ascii name, which all low level LVM commands reference. Additionally, it is the basis for the LVIDs created on that VGID. |
| Logical Volume Control Block (LVCB) | The logical volume control block (lvcb) consists of the first 512 bytes of a logical volume. This area holds important information such as the creation date of the logical volume, information about mirrored copies, and possible mount points in a journaled filesystem. |
| Logical Volume ID (LVID) | The LVID is the soft serial number used to represent the logical volume to the LVM libraries and low level commands. The LVID is created from the VGID of the volume group, a decimal point, and a number which represents the order which the logical volume was created on the volume group. |
Now for the cheet sheet
Directory and Files | |
| Directories and Files | |
Tools | |
| diagnostic | diag - used to hot swap the disk cfgmgr - used mak sure the new disk is seen # to add new disk from the scsi0 controller cfgmgr -l scsi0 |
| Create/Remove hard disk | cfgmgr -l scsi0 mkdev -c disk -l <pv> rmdev -dl <pv> |
Physical Volumes | |
| display | lspv lspv <pv> (detailed) lspv -l <pv> (list logical volumes) lspv -p <pv> (physical partition usage) |
| PVID | chdev -l <pv> -a pv=yes chdev -l <pv> -a pv=clear Note: PVID's are automatically added when the disk is placed into a vg |
| adding | chdev -l <pv> -a pv=yes (new) chpv -v a <pv> (adds back the removed disk) |
| removing | chpv -v r <pv> |
| change physical attributes | chpv -a y <pv> (changes allocatable state to YES) chpv -a n <pv> (changes allocatable state to NO) |
| moving | migratepv <old pv> <new pv> |
Volume Groups | |
| display | lsvg lsvg <vg> (detailed) lsvg -l <vg> (list all logical volumes in goup) lsvg -p <vg> (list all physical volumes in group) lsvg -o (lists all varied on) lsvg -M <vg> (lists assicated disks and state) ## Details volume group info for the hard disk lqueryvg -Atp <pv> lqueryvg -p <disk> -v (Determine the VG ID# on disk) lqueryvg -p <disk> -L (Show all the LV ID#/names in the VG on disk) lqueryvg -p <disk> -P (Show all the PV ID# that reside in the VG on disk) |
| varyon | varyonvg <vg> varyoffvg <vg> Note: the varyon command activiates the volume goup which means it is available for use |
| ODM related | ## Determine if the ODM and VGDA are correct (in sync) getlvodm -u <vg> ## tries to resync VGDA, LV control blocks and ODM synclvodm <vg> ## If the message 0516-366 lsvg: Volume group <vg> is locked is ever seen putlvodm -K `gtlvodm -v <vg>` |
| creating | mkvg -y <vg> -s <PP size> <pv> mkvg -y datavg -s 4 hdisk1 Note: the PP size will be the size of the physical partition size you want 4MB, 8MB |
| extending | extendvg <vg> <pv> |
| reducing | reducevg -d <vg> <pv> ## removes the PVID from the VGDA when a disk has vanished without using the reducevg command reducevg <vg> <PVID> |
| removing | varyoffvg <vg> exportvg <vg> Note: the export command nukes everything regardingthe volume goup in the ODM and /etc/filesystems |
| checking | ## check to see if underlying disk has grown in size Note: use this command if you are using SAN LUN's that have increased in size |
| change volume attributes | ## auto vary on a volume at system start chvg -a y # Turns on/off quorum checking on a volume group chvg -Q [y|n] <vg> |
| renaming | varyoffvg <old vg name> lsvg -p <old vg name> (obtain disk names) exportvg <old vg name> import -y <new vg name> <pv> varyonvg <new vg name> mount -a |
| importing | importvg -y <vg> <pv> importvg <pv> (will use rootvg as default vg) |
| exporting | varyoffvg <vg> exportvg <vg> Note: if the volume has an active paging space this must be turned off before |
Logical Volumes | |
| display | lslv <lv> lslv -l <lv> (list all physical volumes in logical volume) lslv -m <lv> (list ppartition mapping) ## Display lv control block information getlvcb -AT <lv> |
| creating | mklv <vg> <# of PP's> <pv> ## Create a mirrored named logical volume |
| extending | extendlv <lv> <additonal # of PP's> extendlv <lv> <size of volume in B||M|G> |
| reducing/resizing | see filesystem below |
| removing | rmlv <lv> |
| moving | migratepv -l <lv> <old pv> <new pv> |
| adding a mirror to a non-mirrored volume | mklvcopy -s n <lv> <copies 2 or 3> <pv> |
| removing a mirror copy from a mirrored volume | rmlvcopy <lv> <copies 1 or 2> rmlvcopy <lv> <copies 1 or 2> <pv> (specified pv) unmirrorvg <vg> <pv> |
| synchronize logical volume | syncvg -p <pv> syncvg -v <vg> syncvg -l <lv> |
| mirror any unmirrored volumes | mirrorvg <vg> <pv> |
| change volume attributes | ## Enable the bad-block relocation policy chlv -b [y|n] <lv> |
| renaming | chlv -n <new lv name> <old lv name> |
| Miscellaneous | ## Initialises an LV for use as an JFSlog logform </dev/lv> |
Filesystems | |
| display | lsfs lsfs -q <fs> (detailed) Note: use the '-q' to see if the logical volume size is bigger than the filesystem size |
| create | ## create new filesystem, -A means to mount after restart crfs -v jfs -d <lv> -m <mountpoint> -A yes ## Create logical volume, filesystem, mountpoint, add entry to /etc/filesystems at the specified size crfs -v jfs2 -g <vg> -m <mountpoint> -a size=<size in 512k blocks|M|G) -A yes Note: there are two types of filesystems jfs and jfs2, jfs2 allows you to decrease the filesystem size , you cannot reduce a jfs filesystem |
| remove | rmfs <fs> Note: if all filesystems have been removed from a logical volume then the logical volume is removed as well. |
| resize | chfs -a size=<new size> <fs> Note: this will automatically increase or decrease the underlying logical volume as well |
| freeze/unfreeze | chfs -a freeze=<time in seconds> <fs> chfs -a freeze=off <fs> |
| split mirrored copy | chfs -a splitcopy=<split copy mountpoint>-a copy=2 <fs> chfs -a splitcopy=/backup -a copy=2 /testfs |
| change | ## Change the mountpoint chfs -m <new mountpoint> <fs> ## Do not mount after a restart chfs -A no <fs> ## Mount read-only chfs -p ro <fs> |
| mount | mount mount [<fs>|<lv>] mount -a mount all |
| defrag | defragfs -q <fs> (report defrag status) defragfs -r <fs> (runs in report only mode - no action) defragfs <fs> (actually defrags the filesystem) |
| checking and repairing | fsck [-y|-n] <fs> (check a filesystem) fsck -p <fs> (restores primary superblock from backup copy if corrupt) |
Miscellaneous | |
| Complete VG, LV and FS with mirroring example | ## Create the volume group ## Create the jfs2 log logical volume and initialize it this for the volume group |
| Replaced failed mirror drive | ## break the mirror (two ways to do this) rmlvcopy <lv name> 1 <broken disk> unmirrorvg <lv> <broken pv > ## remove the disk from the vg ## remove the hdisk from ODM ## add back to volume group ## create mirror (two ways to do this) |
| Accidently remove a mirrored disk or SAN LUN disappeared off the network | ## This procedure places back a mirror disk that you have accidently pulled or that a SAN LUN disappeared off the network |
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