Tag Archives: lvm

LVM commands tutorial: Part 3: Logical Volume (lvsync, lvlnboot)

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Series of the tutorial to learn LVM commands. In this part, learn how to sync LV and set it as a boot, root, swap device (lvsync, lvlnboot)

This is the last part of LVM command tutorials and last post for logical volume command too. Last all parts of this tutorial can be found on below links :

Let’s start with our first command here.

Command: lvsync

It synchronizes stale PE in given LV. It’s used in mirroring environment. Whenever there is any disk failure or disk path issue, PE goes bad and LV, in turn, has stale PE. Once the issue is corrected we need to sync stale PE with this command if they don’t sync automatically.

The command doesn’t have many options. It should be supplied with the LV path only.

# /usr/sbin/lvsync /dev/vg00/lvol6
Resynchronized logical volume "/dev/vg00/lvol6".

Command: lvlnboot

This command used to define logical volume as a root, dump, swap or boot volume. You have to submit an LV path along with the specific option of your choice to command. Options are as below :

  • -b Boot volume
  • -d Dump volume
  • -r Root volume
  • -s Swap volume
  • -R Recover any missing links
  • -v Verbose mode
# lvlnboot -r /dev/vg00/lvol3
Volume Group configuration for /dev/vg00 has been saved in /etc/lvmconf/vg00.conf
# lvlnboot -b /dev/vg00/lvol1
Volume Group configuration for /dev/vg00 has been saved in /etc/lvmconf/vg00.conf
# lvlnboot -s /dev/vg00/lvol2
Volume Group configuration for /dev/vg00 has been saved in /etc/lvmconf/vg00.conf
# lvlnboot -d /dev/vg00/lvol2
Volume Group configuration for /dev/vg00 has been saved in /etc/lvmconf/vg00.conf

We have already seen this command in root disk mirroring.

This concludes our LVM command tutorials!! Feel free to drop in any queries you have.

LVM commands tutorial: Part 3: Logical Volume (lvextend, lvreduce, lvchange)

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Series of the tutorial to learn LVM commands. In this part, learn how to extend, reduce and change the state of the logical volume (lvextend, lvreduce, lvchange)

In continuation of last part of a logical volume, we will be seeing more commands on lvol in this post. Previous posts of this LVM command tutorial can be found on below links :

Logical volumes like VG can be extended and shrank. We will be seeing lvextend, lvreduce, lvchangecommands in this post.

Command: lvextend

To extend logical volume, you should have enough free space within that VG. Command syntax is pretty much similar to lvcreate command for size. The only thing is you need to supply the final required size in command. For example, the current LV size is 1GB and you want to extend it with 2GB. Then you need to give the final 3GB size in the command argument.

# lvextend -L 3072 /dev/vg01/lvol1
Logical volume "/dev/vg01/lvol1" has been successfully extended.
Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf

Another important option is of mirror copies. It plays a vital role in root disk mirroring. -m is the option with the number of mirror copies as an argument.

# lvextend -m 1 /dev/vg00/lvol1 /dev/disk/disk2_p2
The newly allocated mirrors are now being synchronized. This operation will
take some time. Please wait ....
Logical volume "/dev/vg00/lvol1" has been successfully extended.
Volume Group configuration for /dev/vg00 has been saved in /etc/lvmconf/vg00.conf

Command: lvreduce

This command used for decreasing the number of mirror copies or decreasing the size of LV. This is the data destroying command. Hence make sure you have data of related file system backed up first. The size and mirror copy options are works the same for this command as well. -L for LE_reduce_size, -l number of LE to be reduced and -m is the number of copies to be reduced.

# lvreduce -L 500 /dev/vg01/lvol1
When a logical colume is reduced useful data might get lost;
do you really want the command to proceed (y/n) : y
Logical volume "/dev/vg01/lvol1" has been successfully reduced.
Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf

While reducing mirror copies if one of the PV is failed or missing then command won’t run successfully. you need to supply -k option which will proceed to remove the mirror in case PV is missing.

Command: lvchange

This command is used for changing the characteristics of LV. There are numerous options that can be used.

  • -a y/n Activate or deactivate LV
  • -C y/n Change contiguous allocation policy
  • -D y/n Change distributed allocation policy
  • -p w/r Set permission
  • -t timeout Set timeout in seconds
  • -M y/n Change mirror write cache flag
  • -d p/s Change scheduling policy

This is the end of the second post on LV commands. In the next post, we will see lvsync and lvlnboot commands.

LVM commands tutorial: Part 2: Volume group (vgremove, vgsync)

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Series of the tutorial to learn LVM commands. In this part, learn how to remove volume group from the system and how to sync stale PE within VG (vgremove, vgsync)

This is the fourth and the last post of part two which is related to volume group in our LVM commands tutorial. Rest of the parts and posts can be found in below links :

We have seen 10 commands of volume group activities until now under part two. Now we will cover the remaining two commands in this post.

Command: vgremove

vgremove commands used to remove the volume group from the system. But this is destroying command since it requires removal of all LV, PV in VG. It is always recommended to use vgexport instead of vgremove. Since vgexport also removes VG information from the system but keeps it untouched on PV so that the same PV can be imported to new VG on the new/same system using vgimport.

Safe removal of VG can be done with the below steps :

  1. Backup all user data in that VG
  2. Get information about all LV and PV in that VG using vgdisplay -v command
  3. Make sure no LV is in use using fuser -cu /mount_point command 
    # fuser -cu /data /data:   223412c(user1)
  4. Unmount mount points of related LV 
    # umount /data
  5. Remove all LVs with lvremove /dev/vg01/lvol-name command 
    # lvremove /dev/vg01/lvol1 The logical volume "/dev/vg01/lvol1" is not empty; do you really want to delete the logical volume (y/n) : y Logical volume "/dev/vg01/lvol1" has been successfully removed. Volume Group configuration for /dev/vg03 has been saved in /etc/lvmconf/vg01.conf
  6. Remove all PVs in VG except anyone with vgreduce /dev/vg01 /dev/disk/diskX command 
    #vgreduce /dev/vg01 /dev/disk/disk4 Volume group "/dev/vg01" has been successfully reduced. Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf
  7. Finally, use vgremove command to remove VG from system 
    # vgremove /dev/vg01 Volume group "/dev/vg01" has been successfully removed
  8. Remove related group files from system using rm /dev/vg01 command

Command: vgsync

This command used to sync stale LE of LV mirrors in current VG. This used in mirroring only. One can observe the output of vgdisplay -v and confirm if there are any stale LE in current VG. If you found stale LE then you can synchronize them using this command.

# vgsync /dev/vg01
Resynchronized logical volume "/dev/vg01/lvol01".
Resynchronized logical volume "/dev/vg01/lvol02".
Resynchronized volume group "/dev/vg01".

There are no special options required for this command.

This concludes part two (Volume group) of our LVM tutorials.

LVM commands tutorial : Part 2 : Volume group (vgcfgbackup, vgcfgrestore, vgchange)

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Series of the tutorial to learn LVM commands. In this part, how to backup/restore VG configuration and to change VG state (vgcfgbackup, vgcfgrestore, vgchange)

This is the third post of part 2 in our LVM commands tutorial. In this post, we are going to see how to backup and restore volume group configurations and how to change volume group states i.e. how to activate/de-activate volume group. Other parts of this LVM tutorial can be found on below links :

Volume group configurations play a vital role in moving PV, VG, data across systems. Let’s start with the configuration backup command.

Command: vgcfgbackup

As the command reads, it takes volume group configuration backup into a disk file residing under /etc/lvmconf directory in the file /etc/lvmconf/vg_name.conf. It reads the LVM header details from the system area of the disk and copies it to file. This file helps you to restore configuration on newly added disk in place of the old disk which may have got corrupted or failed.

It is recommended to have this backup taken after every LVM level change. By default all LVM commands altering LVM details are designed to take this backup automatically hence manually running command is not necessary.

To take manual configuration backup use command as below :

# vgcfgbackup /dev/vg01
Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf

This needs to run for every volume group available on the system. This command has a couple of options :

  • -f file Save backup in the file specified rather than the default location
  • -u Only updates extra PV which are added to VG after the last backup. Only new PVs required to be online on the system. If -u not used all PV under VG should be online while running the command.

Command: vgcfgrestore

This command restores the VG configuration taken using the above command. Command mainly needs 2 argument volume group name of which configuration needs to be restored and a PV name on which configuration needs to be restored. There are two things which need to keep in mind.

If PV on which we are restoring the backup is part of the mirror copy, then it should be deactivated first. Then restore back up and reactivate it. Command sequence will be :

# pvchange -a n /dev/disk/disk5
Physical volume "/dev/disk/disk5" has been successfully changed.

# vgcfgrestore -n /dev/vg01 /dev/rdisk/disk5
Volume Group configuration has been restored to /dev/rdisk/disk5

# pvchange -a y /dev/disk/disk5
Physical volume "/dev/disk/disk5" has been successfully changed.

If PV is not a part of the mirror then you should deactivate the volume group first then restore the backup and then activate the volume group again. Command sequence will be :

# vgchange -a n /dev/vg01
Volume group "/dev/vg01" has been successfully changed.

# vgcfgrestore -n /dev/vg01 /dev/rdisk/disk5
Volume Group configuration has been restored to /dev/rdisk/disk5

# vgchange -a y /dev/vg01
Volume group "/dev/vg01" has been successfully changed.

This command has several options which can be used with it :

  • -l List configuration only
  • -F Forcefully restore
  • -f file  Restore the configuration from a specified file, not from default backup location
  • -v Verbose mode
  • -R Forcefully restore even if there is a mismatch between PV in the kernel and in config.
  • -o old_path Restore config saved for old PV (path supplied) to new PV mentioned in the command.

Command: vgchange

This command used to make the volume groups active or inactive. The activated volume group simply means it’s available for use. There are different modes of volume groups in which they can be activated. They can be listed as below :

  1. Normal availability mode
  2. Cluster aware mode
  3. Shareable mode
  4. Quoram requirement mode

vgchange command can be used with specified options and their values to activate or deactivate the volume group. For example to normally activate it should be supplied with the argument -a and its value y. See below output to activate and then deactivate volume group

# vgchange -a y vg01
Volume group “/dev/vg014” has been successfully changed.

# vgchange -a n vg01
Volume group “/dev/vg014” has been successfully changed.

Above stated modes can be activated/deactivated using the below options :

  • -a y/n Normal availability mode
  • -c y/n Cluster aware mode
  • -S y/n Shareable mode
  • -q y/n Quoram requirement mode
  • -p Only activate if all related PVs are online
  • -s Disable stale PE sync
  • -x Cross activate the shareable volume group

This concludes the third post of part two related to the volume group. In the next and last post of part two, we are covering how to remove the volume group from the system and how to sync stale PE within the volume group.

LVM commands tutorial : Part 2 : Volume group (vgextend, vgreduce, vgexport, vgimport)

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Series of the tutorial to learn LVM commands. In this part, how to extend, reduce, export, and import volume group  (vgextend, vgreduce, vgexport, vgimport).

In this post, we are going to see how to extend the volume group, how to reduce the volume group, how to export volume groups, and how to import it. Previous posts of this LVM tutorial series can be found on below links :

This is the second post in part two of the volume group. In previous posts, we have seen commands like vgcreate, vgdisplay and vgscan. Let’s walk through new VG related commands.

Command: vgextend

Whenever there is a need for extra space on mount points and new disks are added to the system, related volume groups need to accommodate these new disks. Let’s say vg01 is existing VG and new disk5 is added to the server then you need to use vgextend command to add these new disks into vg01. This will, in turn, add new free PE in existing VG vg01 and hence free space will hike in VG.

To add disks into existing VG, you need to initialize it first with pvcreate command (see part one tutorial for pvcreate). Once done disk can be used in vgextend like below :

# vgextend /dev/vg01 /dev/disk/disk5
Volume group "/dev/vg01" has been successfully extended.
Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf

After successful completion, you can verify that new PV is added to VG by looking at vgdisplay -v vg01 output.

This command can be used with below options :

  • -f Forcefully extend
  • -x Set allocation permissions
  • -z sparepv Should be used to mirroring to define spare PV
  • -g pvg_name Extend with the physical volume group specified.

Command: vgreduce

Its just reverse of the above command. It reduces VG by removing specified PV in command. It’s a bit risky to use hence extra precaution needed. You should make sure that no PE from targeted PV is being used in any LV of VG. This can be verified by lvdisplay and vgdisplay command. If no then you can use pvmove, lvremove commands to move/delete data. Once you are sure that no PE from targeted PV is being used i.e. all PEs are free to form this PV then run below command to remove PV from VG.

# vgreduce /dev/vg01 /dev/disk/disk5
Volume group "/dev/vg01" has been successfully reduced.
Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf

If you are using multiple PV links then you should remove all PV paths from VG using the above command.

This command allows two options :

  • -f Forcefully remove PV
  • -l pv_path Remove only specified particular PV path from VG

Command: vgexport

Using vgexport one can export all VG related information from disks into map file leaving data on disks intact. With the help of this map file, the same VG can be imported on another system provided all related disks are presented to this another system.

Please note that running this command removes all VG related files from /dev directory and all its related entries in /etc/lvmtab file. This means after running vgexport, that particular VG is turned into non-existent VG for the system.

Before running vgexport, one has to make sure that no one is using data on LVOLs from this VG. This can be verified using fuser -cu /mount_point command. Also, VG shouldn’t be active at the time of export hence you need to de-activate VG using vgchange.

# vgchange -a n /dev/vg01
Volume group "/dev/vg01" has been successfully changed.

# vgexport -v -m /tmp/vg01.map vg01
Beginning the export process on Volume Group "/dev/vg01". 
/dev/dsk/c0t1d0 vgexport:Volume Group “/dev/vg01” has been successfully removed.

This command allows below options :

  • -p Preview only. It won’t actually export Vg but creates a map file. Useful for live VG
  • -v Verbose mode
  • -f file Writes all PV paths to file. This file can be used as input to vgimport.

Command: vgimport

This command imports VG which been exported using the above command. Map file extracted from vgimport command should be supplied as an argument to vgimport. In case if a map file is not available, it will still try to import VG by reading LVM information lies of physical disks. In this case, a list of all PV should be supplied.

After vgimport successfully imports VG, note that it’s in an inactive state. You need to activate VG to use it on the system. Also, its recommended to take a configuration backup once you import new VG on system

# vgimport -v -m /tmp/vg01.map /dev/vg01 list_of_disk
vgimport: Volume group “/dev/vg01” has been successfully created.
Warning: A backup of this volume group may not exist on this machine.
Please remember to take a backup using the vgcfgbackup command after activating the volume group.

# vgchange -a y vg01
Volume group “/dev/vg01” has been successfully changed.

# vgcfgbackup /dev/vg01
Volume Group configuration for /dev/vg01 has been saved in /etc/lvmconf/vg01.conf

This command can be supplied with below options :

  • -N Import with persistent device file names
  • -s Scan each disk
  • -p Preview only
  • -v Verbose mode
  • -f file Import PV paths from the file

This concludes the second post of part two. In the next post, we will be seeing how to backup and restore volume group configurations and how to change volume group states.

LVM commands tutorial : Part 2 : Volume group (vgcreate, vgdisplay, vgscan)

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Series of the tutorial to learn LVM commands. In this part of the tutorial, learn how to create volume groups, and see details of it  (vgcreate, vgdisplay, vgscan).

Today we are starting with part two of the LVM command tutorial series. Other series posts can be found here :

This is the first post of part two which will be taking care of volume group activities. In the following writeup, we are going to see commands on how to create a volume group, how to view details of the volume group and how to scan volume groups to build new /etc/lvmtab file.

Command: vgcreate

As we all know volume group i.e. VG is a collection if PV. Refer to LVM legends for better understanding. VG creation is the next necessary step after PV creation to use disk space in mount points. Since in Unix everything is a file, to manage VG, the kernel creates /dev/vgname/group file. This file represents VG in the kernel. Let us see how to create VG from a bunch of available PV. Post Mar 2008 releases of HPUX creates group file automatically with vgcreate command. But we will see here how to make one.

First, create a directory with the desired name of your VG for example. let’s say testvg is our VG name. After that using mknod command creates a special group file. In command, you need to supply major and minor numbers.

# mkdir /dev/testvg
# mknod /dev/testvg/group c major 0xminor

major number: 64 for version 1.0 VG and 128 for version 2.0 VG
minor number: Its hexadecimal number. 0xnn0000 for v1.0 and 0x0000 for v2.0 where nn/nnn is unique number.

Now that special file is generated go-ahead to create VG

# vgcreate /dev/testvg /dev/disk/disk3 /dev/disk/disk4
Volume group "/dev/testvg" has been successfully created.
Volume Group configuration for /dev/testvg has been saved in /etc/lvmconf/testvg.conf

vgcreate can be run with a single PV argument too. This command has several options as below :

  • -V 1.0            To decide version.
  • -s PE_size    Size of PE to be used in MB. Default is 4MB
  • -e max_PE   Max PE per PV. Default is 1016
  • -l max_lv      Max number of LV per VG. Default is 255
  • -p max_pv   Max number of PV per VG. Default is 255
  • -S vg_size    Max future size of VG. Only in v2.0.

The above options can be supplied to command with proper values but it’s not mandatory. If not supplied then their respective values will be taken into consideration while creating VG. Changes in parameters with these options can be seen in vgdisplay output which you can see incoming section.

Command: vgdisplay

Same as pvdisplay command, vgdisplay is used to view VG details. vgdisplay command can be run with -v option to get more detailed output. If run without -v option then it will show output like below but PV details portion won’t be there.

# vgdisplay -v vg_new
--- Volume groups ---
VG Name                     /dev/testvg
VG Write Access             read/write     
VG Status                   available                 
Max LV                      255    
Cur LV                      0      
Open LV                     0      
Max PV                      16     
Cur PV                      2      
Act PV                      2      
Max PE per PV               6000         
VGDA                        2   
PE Size (Mbytes)            32              
Total PE                    26    
Alloc PE                    0       
Free PE                     26    
Total PVG                   0        
Total Spare PVs             0              
Total Spare PVs in use      0 

   --- Physical volumes ---
   PV Name                     /dev/disk/disk3
   PV Status                   available                
   Total PE                    10       
   Free PE                     10       
   Autoswitch                  On        

   PV Name                     /dev/disk/disk4
   PV Status                   available                
   Total PE                    10       
   Free PE                     10       
   Autoswitch                  On

In the above output, you can see PE Size (Mbytes), Max PE per PV, Max LV, Max PV fields which can be altered with options -s, -e, -l, -p arguments in vgcreate command we saw above.  The above output is pretty self-explanatory. It also shows PV details which are part of this VG.

Command: vgscan

This command used for scanning all available PVs to get information on VG and related LV’s and rebuild /etc/lvmtab file. This command used the below options :

  • -a Scan all available PV paths.
  • -B Write all persistent and legacy paths to /etc/lvmtab file
  • -f vg_name Force to update entries of existing VG in /etc/lvmtab with updated info, if any
  • -k Avoid probing disks. Build file from kernel known structure.
  • -N Populate the file with persistent DSF names
  • -p Preview mode only. It won’t update lvmtab file
  • -v verbose mode. Prints messages in the console.
# vgscan -v
/dev/vg00
/dev/disk/disk1_p2
/dev/disk/disk2_p2

Scan of Physical Volumes Complete.

Normally we use vgscan -v only. After this command, you can verify the timestamp of /etc/lvmtab file to verify it’s been updated.

This concludes the first 3 commands of VG. In the next post, we will see how to extend the volume group, how to reduce the volume group and how to export/import volume groups.

Basics of LVM legends

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Get acquainted with LVM (Logical Volume Manager) terms. Learn what is physical volume, logical volume, physical extent, volume group, and logical extent.

LVM (logical volume manager) legends

PV is a Physical Volume

Any single disk / LUN on the system is identified as PV. It can be raw or formatted with a file system. Raw PV is referred to as /dev/rdsk/c0t0d1 (legacy) or /dev/rdisk/disk1 (agile) whereas formatted one is referred to as  /dev/dsk/c0t0d1 (legacy) or /dev/disk/disk1 (agile). Check PV name in below output as a formatted device.

# vgdisplay -v vg00

--- Volume groups ---
VG Name                     /dev/vg00
VG Write Access             read/write
VG Status                   available
Max LV                      255
Cur LV                      13
Open LV                     13
Max PV                      16
Cur PV                      1
Act PV                      1
Max PE per PV               4355
VGDA                        2
PE Size (Mbytes)            32
Total PE                    4345
Alloc PE                    4303
Free PE                     42
Total PVG                   0
Total Spare PVs             0
Total Spare PVs in use      0

   --- Logical volumes ---
   LV Name                     /dev/vg00/lvol1
   LV Status                   available/syncd
   LV Size (Mbytes)            1024
   Current LE                  32
   Allocated PE                32
   Used PV                     1

   --- Physical volumes ---
   PV Name                     /dev/dsk/c3t0d0s2
   PV Status                   available
   Total PE                    4345
   Free PE                     42
   Autoswitch                  On
   Proactive Polling           On
Physical volume naming conventions :

/dev/rdsk/cxtxdx – Legacy character device file
/dev/rdsk/cxtxdxs2 – Legacy character device file, partition 2
/dev/dsk/cxtxdx – The legacy block device file
/dev/dsk/cxtxdxs2 – Legacy block device file, partition 2
/dev/rdisk/diskx – The persistent character device file
/dev/rdisk/diskx_p2 – Persistent character device file, partition 2
/dev/disk/diskx – The persistent block device file
/dev/disk/diskx_p2 – Persistent block device file, partition 2

PE is Physical Extent

Its smallest chunk of PV can be used as a block under the file system. PV is consists of the number of PEs. We always use PV names while using LVM commands. In the above example, PE size is set to 32MB & a total of 4345 PEs are available on disk.

Read our LVM tutorials: LVM cheat sheet.

VG is Volume Group

One or more PV come together to form a Volume Group. This grouping enables to slice down combined
storage capacity of disks to our choice of small volumes. In the above example, vg00 is volume group made up of single PV & it’s sliced down to 8 LV (only one shown in above example)

LV is the Logical Volume

Its a slice of volume group using some capacity of PV to form a smaller volume. Its basically used as a mount point /swap like drives (C:, D:) in Windows. We can see one LV in above example and its details.
LE is Logical Extent.
Same as PE, LE is the smallest chunk of LV.

Below tables gives you an idea about some numbers related to them:

LVs per VG range: 1-255, default: 255
PVs per VG range: 1-255, default: 16
PEs per VG   range : 1-66535 default : 1016

with the above table, as max PE size is 64MB and 66,535 PEs max per VG, one can create a max of 64×66353=4TB of the file system.