rhcsa-study-guide
README

4.b Create and remove physical volumes
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Logical Volume Manager
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Logical Volume Manager (LVM) is a device mapper target that provides logical volume management for the Linux kernel. LVM allows a pool of space to manage storage.

  • PV - Physical Volumes are directly related to hard drives or partitions
  • VG - A Volume Group can have multiple physical Volumes
  • LV - A Logical Volume sits inside a Volume Group and it's what is assigned to a file system (/root, /home, etc...)

When a physical disk is setup for LVM, metadata is written at the beginning of the disk for normal usage, and at the end of the disk for backup usage.

Steps of Creating a Physical Volume
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First create initialize the disks to be used by LVM with pvcreate (Initialize physical volume(s) for use by LVM)

# pvcreate /dev/device /dev/device2 /dev/device3

Then we create a volume group with vgcreate (Create a volume group)

# vgcreate [vg name] /dev/device /dev/device2 /dev/device3

Optionally use the '-s' switch to set the Physical Extent size (for LVM2, the only effect this flag has is that when using too many physical volumes, the LVM tools will perform better)

And finally create the Logical Volume (4GB)

# lvcreate -L 4g [vg name] -n [lv name]

Flags:

  • -n - set the Logical Volume name
  • -l - use extents rather than a specified size

Create the file system

# mkfs.xfs /dev/[vgname]/[lvname]

Creating and Deleting Physical Volumes
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Commands:

  • lvm (8) - LVM2 tools
  • pvcreate (8) - Initialize physical volume(s) for use by LVM
  • pvdisplay (8) - Display various attributes of physical volume(s)
  • pvremove (8) - Remove LVM label(s) from physical volume(s)
  • pvs (8) - Display information about physical volumes

Creating Physical Volumes
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Physical volumes can be created using full disks or partitions.

# pvcreate /dev/part1 /dev/part2

Or

# pvcreate /dev/sdb /dev/sdc

Deleting Physical Volumes
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pvremove wipes the label on a device so that LVM will no longer recognize it as a PV. A PV cannot be removed from a VG while it is used by an active LV.

Removing a PV

# pvremove /dev/sdb /dev/sdc
Labels on physical volume "/dev/sdb" successfully wiped.
Labels on physical volume "/dev/sdc" successfully wiped.

Trying to remove a PV that has a VG and LV

# pvremove /dev/sdb /dev/sdc
  PV /dev/sdb is used by VG testvg so please use vgreduce first.
  (If you are certain you need pvremove, then confirm by using --force twice.)
  /dev/sdb: physical volume label not removed.
  PV /dev/sdc is used by VG testvg so please use vgreduce first.
  (If you are certain you need pvremove, then confirm by using --force twice.)
  /dev/sdc: physical volume label not removed.

You can try to force remove with -ff

# pvremove -ff /dev/sdb /dev/sdc
  WARNING: PV /dev/sdb is used by VG testvg.
Really WIPE LABELS from physical volume "/dev/sdb" of volume group "testvg" [y/n]? y
  WARNING: Wiping physical volume label from /dev/sdb of volume group "testvg".
  WARNING: PV /dev/sdc is used by VG testvg.
Really WIPE LABELS from physical volume "/dev/sdc" of volume group "testvg" [y/n]? y
  WARNING: Wiping physical volume label from /dev/sdc of volume group "testvg".
Table Of Contents

4.b Create and remove physical volumes

Logical Volume Manager

Steps of Creating a Physical Volume

Creating and Deleting Physical Volumes

Creating Physical Volumes

Deleting Physical Volumes