managing_lv.txt

Ch.7 - Managing Logical Volumes

LVMs makes managing disk space easier.

Hierarchy:

-Physical Devices --> Physical Volumes(PVs) --> Volume Groups(VGs) --> Logical Volumes(LVs)

Creating LVM storage requires several steps. 
1.Determine which physical devices to use. 
2.Initialize your device(s) as a physical volume(s) so that  they are recognized as belonging to LVM. 
3.Combine the physical volume(s) into a volume group.
(This creates a pool of disk space out of which logical volumes can be allocated.)

*Logical volumes created from the available space in a volume group can be formatted with a file system, activated as swap space, and mounted or activated persistently.) 



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Creating Logical Volumes

Steps:

1.Prepare the physical device

Use parted, gdisk, or fdisk to create a new partition for use with LVM. 
  Always set the partition type to Linux LVM on LVM partitions
  Ex: 
   -[root@host ~]# parted -s /dev/vdb mkpart primary 1MiB 769MiB
   -[root@host ~]# parted -s /dev/vdb mkpart primary 770MiB 1026MiB
   -[root@host ~]# parted -s /dev/vdb set 1 lvm on
   -[root@host ~]# parted -s /dev/vdb set 2 lvm on  

**A physical device only needs to be prepared if there are none prepared already and a new physical volume is 
  required to create or extend a volume group.

2.Create a physical volume
  Ex: 
   - pvcreate /dev/vdb2 /dev/vdb1
  
(This labels the devices /dev/vdb2 and /dev/vdb1 as PVs, ready for allocation into a volume group.)
*A PV only needs to be created if there are no PVs free to create or extend a VG.

3.Create a volume group
  Ex: 
   - vgcreate vg01 /dev/vdb2 /dev/vdb1

**vg01 is the vg_name
(This creates a VG called vg01 that is the combined size, in PE units, of the two PVs /dev/vdb2 and /dev/vdb1.)

4.Create a logical volume
  Ex: 
   - lvcreate -n lv01 -L 700M vg01

(This creates an LV called lv01, 700 MiB in size, in the VG vg01.)

Notes:
**lv01 is the lv_name
**the -n option to set the LV name, 
**the -L option to set the LV size in bytes or the -l option to set the LV size in extents, 
**the name of the volume group hosting this logical volume.(vg01)

5.Add the file system and make it available across reboots
  Ex: 
   a. mkfs -t xfs /dev/vg01/lv01
   b. mkdir /mnt/data
   c. /dev/vg01/lv01  /mnt/data xfs  defaults 1 2 
     (add this entry to /etc/fstab file)
   d. mount /mnt/data
     (to mount the file system that you just added in /etc/fstab)
   e. systemctl daemon-reload

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Removing a Logical Volume

Important!!!
**Back up or move your data before you remove the logical volume otherwise you may destroy any data stored on the LV.

1.Prepare the file system
  Ex:
   - umount /mnt/data

2.Remove the LV
  Ex:
   - lvremove /dev/vg01/lv01 

(Use lvremove DEVICE_NAME to remove a logical volume that is no longer needed.)

3.Remove the VG
  Ex:
   - vgremove vg01

(Use vgremove VG_NAME to remove a volume group that is no longer needed.)

4.Remove the PV
  Ex:
   - pvremove /dev/vdb2 /dev/vdb1

(Use pvremove to remove physical volumes that are no longer needed.)

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Reviewing LVM Status Information

1.Physical Volumes
  Ex: 
   - pvdisplay /dev/vdb1

(Use pvdisplay to display information about physical volumes.)

2.Volume Groups 
  Ex:
   - vgdisplay vg01

(Use vgdisplay to display information about volume groups.)

3.Logical Volumes
  Ex: 
   - lvdisplay /dev/vg01/lv01

(Use lvdisplay to display information about logical volumes.)

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Extending and Reducing a Volume Group

1.Extend a volume group (VG) using pvcreate and vgextend, 
  and use vgdisplay to verify the results.
  Ex:
   a. pvcreate
   b. vgextend
   c. vgdisplay

2.Reduce a VG using pvmove and vgreduce.
  Ex: 
   a. pvmove
   b. vgreduce

3.Extend a logical volume (LV) using lvextend.
  Ex:
   - lvextend

4.Resize XFS file systems with xfs_growfs.
  Ex:
   - xfs_growfs

5.Resize ext4 file systems with resize2fs.
  Ex:
   - resize2fs


Extending a Volume Group:

Steps:

1.Prepare the physical device and create the physical 
  volume.
  Ex:
   a.parted -s /dev/vdb mkpart primary 1027MiB 1539MiB
   b.parted -s /dev/vdb set 3 lvm on
   c.pvcreate /dev/vdb3 

2.Extend the volume group.
  Ex:
   - vgextend vg01 /dev/vdb3 

3.Verify that the new space is available.
  Ex:
   - vgdisplay vg01 
**Use vgdisplay to confirm the additional physical extents are available. 
  Inspect the Free PE / Size in the output. It should not be zero.

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Reducing a Volume Group

Steps:

1.Move the physical extents.
  Ex:
   - pvmove /dev/vdb3

**This command moves the PEs from /dev/vdb3 to other PVs with free PEs in the same VG.
**Before using pvmove, back up data stored on all logical volumes in the volume group.

2.Reduce the volume group.
  Ex:
   - vgreduce vg01 /dev/vdb3

**This removes the /dev/vdb3 PV from the vg01 VG and it can now be added to another VG. 
  Alternatively, pvremove can be used to permanently stop using the device as a PV. 

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Extending a Logical Volume and XFS File System

Extending a Logical Volume

1.Verify that the volume group has space available.
  Ex:
   - vgdisplay vg01

Notes:
Inspect the Free PE/Size in the output. Confirm that the volume group has sufficient 
free space for the LV extension. If insufficient space is available, then extend the 
volume group appropriately.

2.Extend the logical volume.
  Ex: 
   - lvextend -L +300M /dev/vg01/lv01

**This increases the size of the logical volume lv01 by 300 MiB.
**As with lvcreate, different methods exist to specify the size: the -l option expects the 
  number of physical extents as the argument. The -L option expects sizes in bytes, mebibytes, 
  gibibytes, and similar.

3.Extend the file system.
  Ex:
   - xfs_growfs /mnt/data

**Use xfs_growfs mountpoint to expand the file system to occupy the extended LV.

Notes:
An alternative to running the two steps consecutively is to include the -r option with the 
lvextend command. This resizes the file system after the LV is extended, using fsadm(8).

Ex:
   - lvextend -r -L +300M /dev/vg01/lv01

4.Verify the new size of the mounted file system.
  Ex:
   - df -h /mountpoint

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Extending a Logical Volume and ext4 File System

See steps 1 and 2 as above.

3.Extend the file system.
  Ex:
   - resize2fs /dev/vg01/lv01

**Use resize2fs /dev/vgname/lvname to expand the file system to occupy the new extended LV.

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Extend a Logical Volume and Swap Space

1.Verify the volume group has space available.

  **Use vgdisplay vgname to verify that a sufficient number of free physical extents are available.

2.Deactivate the swap space.
  
  **Use swapoff -v /dev/vgname/lvname to deactivate the swap space on the logical volume.

3.Extend the logical volume.

  **lvextend -l +extents /dev/vgname/lvname extends the logical volume /dev/vgname/lvname by the extents value.

4.Format the logical volume as swap space.

  **mkswap /dev/vgname/lvname formats the entire logical volume as swap space.

5.Activate the swap space.

  **Use swapon -va /dev/vgname/lvname to activate the swap space on the logical volume.