LVM: Logical Volume Manager - Revision history

Benrwong: /* LVM Live Snapshot */

2017-10-23T00:00:48Z

LVM Live Snapshot

← Older revision		Revision as of 00:00, 23 October 2017
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	==LVM Live Snapshot==		==LVM Live Snapshot==
	Live logical volume snapshots are a way for us to back up files that are constantly changing (such as VMs and databases). ~~When a~~ logical volume snapshot contains all data when the snapshot was created. The data in the snapshot does not change ~~so it can be backed up~~. When an LV snapshot is created, a new logical volume becomes available for you to mount. Once the snapshot is mounted, all the data can be accessed and then backed up, separate from the original data which might continue to change.		Live logical volume snapshots are a way for us to back up files that are constantly changing (such as VMs and databases). A logical volume snapshot contains all data when the snapshot was created. The data in the snapshot does not change but the data the snapshot is based on is allowed to continue changing. When an LV snapshot is created, a new logical volume becomes available for you to mount. Once the snapshot is mounted, all the data can be accessed and then backed up, separate from the original data which might continue to change.

	Example:		Example:

Benrwong: Included section about how to reduce logical volumes

2017-10-11T18:23:20Z

Included section about how to reduce logical volumes

@@ Line 100: / Line 100: @@
    /dev/mapper/vg_system-lv_root
 G   11G   19G  36% /
 ==LVM Live Snapshot==

Benrwong: /* LVM Live Snapshot */ added how to remove logical volume snapshot

2017-10-10T17:41:58Z

LVM Live Snapshot: added how to remove logical volume snapshot

← Older revision		Revision as of 17:41, 10 October 2017
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	6) While the snapshot is active, backup the snapshot images with your backup tool of choice.		6) While the snapshot is active, backup the snapshot images with your backup tool of choice.
	'''[root@vav backups]# tar -czvf nu_vm_images-20171009.tar /root/image-backups/nu-disk1.qcow2'''		'''[root@vav backups]# tar -czvf /tmp/nu_vm_images-20171009.tar /root/image-backups/nu-disk1.qcow2'''
	tar: Removing leading '/' from member names		tar: Removing leading '/' from member names
	/root/image-backups/nu-disk1.qcow2		/root/image-backups/nu-disk1.qcow2
			'''-sh-4.1$ ls /tmp'''
			BES hsperfdata_root '''nu_vm_image-2017.tar''' orbit-root orbit-s_bwong1
			7) Once the backup is done, we don't need the live snapshot anymore. You can umount it and lvremove the logical volume we made in the steps.
			'''[root@vav ~]# umount /root/image-backups/'''
			'''[root@vav ~]# lvremove /dev/vg_data/lv_images_snap'''
			Do you really want to remove active logical volume lv_images_snap? [y/n]: y
			Logical volume "lv_images_snap" successfully removed


	Other Reference: http://www.tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html		Other Reference: http://www.tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html

Benrwong: /* Intro */

2017-10-10T17:24:38Z

Intro

← Older revision		Revision as of 17:24, 10 October 2017
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	Here's some basic information to get you started with the VM tau used as the example:		Here's some basic information to get you started with the VM tau used as the example:

	'''Physical Volume''' - are physical (or virtual if they are VM images) disk drives. LVM will not recognize ~~them~~ unless they are declared to be allocated for LVM usage using the 'pvcreate' command.		'''Physical Volume''' - are physical (or virtual if they are VM images) disk drives. LVM will not recognize attached disk drives unless they are declared to be allocated for LVM usage using the 'pvcreate' command.
	Use command 'pvs' to see the physical volumes that have been allocated to lvm:		Use command 'pvs' to see the physical volumes that have been allocated to lvm:
	[root@tau ~]# pvs		[root@tau ~]# pvs
Line 25:		Line 25:
	lv_root vg_system -wi-ao---- 31.31g		lv_root vg_system -wi-ao---- 31.31g
	lv_swap vg_system -wi-ao---- 3.50g		lv_swap vg_system -wi-ao---- 3.50g


	==Rules to Remember about LVM==		==Rules to Remember about LVM==

Benrwong: /* LVM Live Snapshot */

2017-10-10T17:20:27Z

LVM Live Snapshot

← Older revision		Revision as of 17:20, 10 October 2017
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	6) While the snapshot is active, backup the snapshot images with your backup tool of choice.		6) While the snapshot is active, backup the snapshot images with your backup tool of choice.
	'''[root@vav backups]# tar -czvf nu_vm_images-20171009.tar /root/image-backups/'''		'''[root@vav backups]# tar -czvf nu_vm_images-20171009.tar /root/image-backups/nu-disk1.qcow2'''
			tar: Removing leading '/' from member names
			/root/image-backups/nu-disk1.qcow2
			Other Reference: http://www.tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html

Benrwong: Added entire section regarding the use of LVM snapshot. This tool will allow us an easy way to backup VM images without pausing/stopping the VMs.

2017-10-10T00:01:29Z

Added entire section regarding the use of LVM snapshot. This tool will allow us an easy way to backup VM images without pausing/stopping the VMs.

@@ Line 97: / Line 97: @@
    The filesystem on /dev/mapper/vg_system-lv_root is now 8208384 blocks long.
 ) Then everything should be swell!
-   [root@tau usr]# df -h .
+   '''[root@tau usr]# df -h .'''
    Filesystem            Size  Used Avail Use% Mounted on
    /dev/mapper/vg_system-lv_root
 G   11G   19G  36% /

Benrwong at 22:26, 18 April 2017

2017-04-18T22:26:38Z

← Older revision		Revision as of 22:26, 18 April 2017
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	'''Volume Group''' - a group of physical volumes that are linked together under a single name.		'''Volume Group''' - a group of physical volumes that are linked together under a single name.
	Use command 'vgs' to see volume groups. The number of Physical Volumes is 2 because both /dev/vda2 and /dev/vdb1 are under this group, vg_system. Because vg_system is a grouping of /dev/vda2 and /dev/vdb1, the volume group's size is the sum of the physical size of the two physical disk partitions.		Use command 'vgs' to see volume groups. The number of Physical Volumes is 2 because both /dev/vda2 and /dev/vdb1 are under this group, vg_system.
			Because vg_system is a grouping of /dev/vda2 and /dev/vdb1, the volume group's size is the sum of the physical size of the two physical disk partitions.
	[root@tau ~]# vgs		[root@tau ~]# vgs
	VG #PV #LV #SN Attr VSize VFree		VG #PV #LV #SN Attr VSize VFree

Benrwong: Created page on Logical Volume Manager basics. Also includes a quick example on expanding a logical volume

2017-03-29T18:26:59Z

Created page on Logical Volume Manager basics. Also includes a quick example on expanding a logical volume

New page

LVM provides some great uses such as creating a single logical volume out of multiple hard disks (similar to RAID 0) and letting you expand or reduce filesystems and disk sizes of logical volumes even while the disks are live and operational. But care needs to be taken in understanding how to execute these procedures because you can accidentally delete data if you are not careful.

==Intro==

Here's some basic information to get you started with the VM tau used as the example:

'''Physical Volume''' - are physical (or virtual if they are VM images) disk drives. LVM will not recognize them unless they are declared to be allocated for LVM usage using the 'pvcreate' command.
Use command 'pvs' to see the physical volumes that have been allocated to lvm:
[root@tau ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/vda2 vg_system lvm2 a--u 14.84g 0
/dev/vdb1 vg_system lvm2 a--u 19.97g 0

'''Volume Group''' - a group of physical volumes that are linked together under a single name.
Use command 'vgs' to see volume groups. The number of Physical Volumes is 2 because both /dev/vda2 and /dev/vdb1 are under this group, vg_system. Because vg_system is a grouping of /dev/vda2 and /dev/vdb1, the volume group's size is the sum of the physical size of the two physical disk partitions.
[root@tau ~]# vgs
VG #PV #LV #SN Attr VSize VFree
vg_system 2 2 0 wz--n- 34.81g 0

'''Logical Volume''' - A logical partition of a volume group. All logical volumes are listed under the directory /dev/mapper.
Use command 'lvs' to see logical volumes. Under here, I have two logical volumes under volume group vg_system.
[root@tau ~]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
lv_root vg_system -wi-ao---- 31.31g
lv_swap vg_system -wi-ao---- 3.50g

==Rules to Remember about LVM==
1) Think of Logical Volumes as a container and the filesystem is the contents. If you wish to reduce a logical volume size, you must reduce the filesystem's size first if you can. Reducing a logical volume size before reducing the filesystem's size will lead to the lost data! (It would be like having a full cup of water then reducing the size of your cup) <br />
2) The opposite holds true. If you wish to expand a logical volume, expand the logical volume and then expand the filesystem or else the size will remain the same! Use the command resize2fs. <br />
3) To summarize LVM:
a) Physical volumes are disks or disk partitions that are initialized to be used by LVM.
b) Physical volumes form a volume group.
c) Logical volumes are partitions of volume groups.
d) Filesystems are placed in logical volumes.
==Expanding a Logical Volume After Adding a New Physical/Virtual Disk==
Here's the steps I took to increase the logical volume size of the VM Tau:

1) Tau's root directory was previously 11.34 Gbs which was too small and kept filling up. From this command, I can see / belongs to a logical volume because its filesystem exists on /dev/mapper.
[root@tau usr]# df -hl
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_system-lv_root
12G 11G 41M 100% /
tmpfs 1.9G 0 1.9G 0% /dev/shm
/dev/vda1 146M 102M 37M 74% /boot

[root@tau usr]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
lv_root vg_system -wi-ao---- 11.34g
lv_swap vg_system -wi-ao---- 3.50g
2) I listed out the existing physical volumes and volume groups using the command 'pvs' and 'vgs' to take into account what existed already. I could see we were using one disk partition /dev/vda2 as the physical volume and it belonged to the volume group 'vg_system'
[root@tau usr]# pvs
PV VG Fmt Attr PSize PFree
/dev/vda2 vg_system lvm2 a--u 14.84g 0
[root@tau usr]# vgs
VG #PV #LV #SN Attr VSize VFree
vg_system 1 2 0 wz--n- 14.84g 0
3) I had a disk partition /dev/vdb1 which was added but unused. Since it was free, I first initialized it to be an LVM physical volume.
'''[root@tau usr]# pvcreate /dev/vdb1'''
Physical volume "/dev/vdb1" successfully created
[root@tau ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/vda2 vg_system lvm2 a--u 14.84g 0
/dev/vdb1 vg_system lvm2 a--u 19.97g 0
4) I added the new physical volume, /dev/vdb1, to the existing volume group vg_system. You can see the size of the volume group extends after I did vgextend.
[root@tau usr]# vgs
VG #PV #LV #SN Attr VSize VFree
vg_system 1 2 0 wz--n- 14.84g 0
'''[root@tau usr]# vgextend vg_system /dev/vdb1'''
Volume group "vg_system" successfully extended
[root@tau usr]# vgs
VG #PV #LV #SN Attr VSize VFree
vg_system 2 2 0 wz--n- 34.81g 19.97g
5) After the volume group expanded, next comes the logical volume. I issued the command to resize the logical volume lv_root to fill up all the free space in the volume group vg_system
[root@tau usr]# lvs
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert
lv_root vg_system -wi-ao---- 11.34g
lv_swap vg_system -wi-ao---- 3.50g
'''[root@tau usr]# lvextend --verbose -l +100%FREE /dev/vg_system/lv_root'''
Using volume group(s) on command line.
Converted 100%FREE into at most 639 physical extents.
Archiving volume group "vg_system" metadata (seqno 5).
Extending logical volume vg_system/lv_root to up to 31.31 GiB
Size of logical volume vg_system/lv_root changed from 11.34 GiB (363 extents) to 31.31 GiB (1002 extents).
Loading vg_system-lv_root table (253:0)
Suspending vg_system-lv_root (253:0) with device flush
Resuming vg_system-lv_root (253:0)
Creating volume group backup "/etc/lvm/backup/vg_system" (seqno 6).
Logical volume lv_root successfully resized.
6) Lastly, we need to resize the filesystem that resides on logical volume lv_root.
'''[root@tau usr]# resize2fs /dev/mapper/vg_system-lv_root'''
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/mapper/vg_system-lv_root is mounted on /; on-line resizing required
old desc_blocks = 1, new_desc_blocks = 2
Performing an on-line resize of /dev/mapper/vg_system-lv_root to 8208384 (4k) blocks.
The filesystem on /dev/mapper/vg_system-lv_root is now 8208384 blocks long.
7) Then everything should be swell!
[root@tau usr]# df -h .
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/vg_system-lv_root
31G 11G 19G 36% /