Encrypted volumes part 1 / LVM

Toni Sredanović · January 11, 2024

LVM   Physical   Logical   Disk

Encrypted volumes part 1 / LVM

Logical Volume Manager (LVM) is used to create logical volumes (think of it as virtual disks/partitions) from multiple physical volumes (disk partitions or entire disks).

In this post (part 1) we will focus on creating a single logical volume from multiple hard disks and in the next post (part 2) we will see how to encrypt that logical volume.

With that in mind there are 3 main aspects of LVM:

  1. Physical volumes - hard disks/partitions
  2. Volume groups - used for grouping physical volumes
  3. Logical volumes - contain defined size available from a volume group

1. Physical volumes

Let’s start off by listing all disks available on the system using the fdisk command and identifing which of them we want to add to our logical volume:

fdisk -l

In this example we have /dev/sda and /dev/sdb:

Disk /dev/sda: 465.76 GiB, 500107862016 bytes, 976773168 sectors
Disk model: nal USB 3.0
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0x4df08fa8

Disk /dev/sdb: 3.64 TiB, 4000752599040 bytes, 7813969920 sectors
Disk model: My Passport 2627
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes

We can remove all partitions from them (replace sdx with sda and sdb):

fdisk /dev/sdx
  • delete partiton with d command
  • verify deletion with p command
  • confirm with w command

And remove any metadata (replace sdx with sda and sdb):

wipefs --all --backup /dev/sdx

Finally mark the disks as LVM physical volumes:

pvcreate /dev/sda /dev/sdb

To verify we can use the lvmdiskscan command:

lvmdiskscan

Among everything it shows there should be:

  /dev/sda       [     465.76 GiB] LVM physical volume
  /dev/sdb       [      <3.64 TiB] LVM physical volume

2. Volume groups

To create a volume group simply use the vgcreate command, in this example the volume group will be called vg0 and it will contain /dev/sda and /dev/sdb physical volumes:

vgcreate vg0 /dev/sda /dev/sdb

Verify with the pvs command:

pvs

We should see both /dev/sda and /dev/sdb physical volumes in the vg0 volume group:

  PV         VG  Fmt  Attr PSize    PFree
  /dev/sda   vg0 lvm2 a--  <465.76g <465.76g
  /dev/sdb   vg0 lvm2 a--    <3.64t   <3.64t

3. Logical volumes

Finally we get to creating a logical volume, in this example we will create one named lv0 with 100% of the available space from our vg0 volume group:

lvcreate -l 100%FREE -n lv0 vg0

To verify we can use the lvdisplay command:

lvdisplay

And there we have it, our lv0 logical volume with size equal to two of our disks combined:

  --- Logical volume ---
  LV Path                /dev/vg0/lv0
  LV Name                lv0
  VG Name                vg0
  LV UUID                BepI42-1dx6-3I0K-fpLV-qUNk-euW5-c3r1GL
  LV Write Access        read/write
  LV Creation host, time server-rpi4, 2024-01-10 13:18:35 +0100
  LV Status              available
  # open                 0
  LV Size                4.09 TiB
  Current LE             1073087
  Segments               2
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0

Useful commands

Some other commands we might find useful, especially if messing up something while following this post:

Delete a logical volume (use LV Path from lvdisplay command):

lvremove /dev/vg0/lv0

Delete a volume group:

vgremove vg0

Delete a physical volume (replace sdx with sda or sdb):

pvremove /dev/sdx

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