q18-lvm-storage

Énoncé§

Solve this question on: terminal

You’re required to perform changes on LVM volumes:

1. Reduce the volume group vol1 by removing disk /dev/vdh from it
2. Create a new volume group named vol2 which uses disk /dev/vdh
3. Create a 50M logical volume named p1 for volume group vol2
4. Format that new logical volume with ext4

Solution§

Some helpful abbreviations when working with LVM, because command names usually start with those:

PV = Physical Volume

VG = Volume Group

LV = Logical Volume

Start by having a look at PVs:

sudo pvs
  PV         VG        Fmt  Attr PSize    PFree
  /dev/vda3  ubuntu-vg lvm2 a--  <126.00g 63.00g
  /dev/vdg   vol1      lvm2 a--    96.00m 84.00m
  /dev/vdh   vol1      lvm2 a--    96.00m 96.00m

In the output above we can see that the VG vol1 uses two disks /dev/vdg and /dev/vdh. We can also get an overview over all system disks and their LVM usage:

sudo lvmdiskscan
  /dev/loop0 [     <49.84 MiB]
  /dev/loop1 [      63.28 MiB]
  /dev/loop2 [    <111.95 MiB]
  /dev/vda2  [       2.00 GiB]
  /dev/loop3 [     <53.26 MiB]
  /dev/vda3  [    <126.00 GiB] LVM physical volume
  /dev/loop4 [      63.45 MiB]
  /dev/vdb   [     100.00 MiB]
  /dev/vdc   [     100.00 MiB]
  /dev/vdd   [     100.00 MiB]
  /dev/vde   [     100.00 MiB]
  /dev/vdf   [     100.00 MiB]
  /dev/vdg   [     100.00 MiB] LVM physical volume # disk 1
  /dev/vdh   [     100.00 MiB] LVM physical volume # disk 2
  5 disks
  6 partitions
  2 LVM physical volume whole disks
  1 LVM physical volume

The existing PV /dev/vda3 with VG ubuntu-vg is created by the main operating system and shouldn’t be touched.

Step 1§

We want to remove disk /dev/vdh from the existing VG vol1:

sudo vgs # list all VGs
  VG         PV  LV  SN Attr   VSize    VFree
  ubuntu-vg   1   1   0 wz--n- <126.00g  63.00g
  vol1        2   1   0 wz--n-  192.00m 180.00m # two PVs
sudo vgreduce vol1 /dev/vdh
  Removed "/dev/vdh" from volume group "vol1"
sudo vgs
  VG         PV  LV  SN Attr   VSize    VFree
  ubuntu-vg   1   1   0 wz--n- <126.00g 63.00g
  vol1        1   1   0 wz--n-   96.00m 84.00m  # one PV

That should do it. We can also verify this by listing all PVs:

sudo pvs
  PV         VG        Fmt  Attr PSize    PFree
  /dev/vda3  ubuntu-vg lvm2 a--  <126.00g  63.00g
  /dev/vdg   vol1      lvm2 a--    96.00m  84.00m
  /dev/vdh             lvm2 ---   100.00m 100.00m # not assigned to a VG any longer

Step 2§

Now we’re going to create a new PV using that now free disk:

sudo vgcreate vol2 /dev/vdh
  Volume group "vol2" successfully created
sudo pvs
  PV         VG        Fmt  Attr PSize    PFree
  /dev/vda3  ubuntu-vg lvm2 a--  <126.00g 63.00g
  /dev/vdg   vol1      lvm2 a--    96.00m 84.00m
  /dev/vdh   vol2      lvm2 a--    96.00m 96.00m # assigned to the VG

Step 3§

We continue by creating a LV for our new VG:

sudo lvs # no LV yet for vol2
  LV        VG        Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  ubuntu-lv ubuntu-vg -wi-ao---- <63.00g
  p1        vol1      -wi-a-----  12.00m
sudo lvcreate --size 50M --name p1 vol2
  Rounding up size to full physical extent 52.00 MiB
  Logical volume "p1" created.
sudo lvs
  LV        VG        Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  ubuntu-lv ubuntu-vg -wi-ao---- <63.00g
  p1        vol1      -wi-a-----  12.00m
  p1        vol2      -wi-a-----  52.00m  # there we go

Step 4§

We can access LVM partitions or LVs in the usual way once we know the path:

sudo mkfs -t ext4 /dev/vol2/p1
mke2fs 1.46.5 (30-Dec-2021)

Creating filesystem with 13312 4k blocks and 13312 inodes

Allocating group tables: done

Writing inode tables: done

Creating journal (1024 blocks): done

Writing superblocks and filesystem accounting information: done

We could now go ahead and mount and use /dev/vol2/p1 as we’re used to.

Extending a LV

Also interesting and could also be part of the exam is extending a mounted LV:

sudo mkdir /mnt/vol2_p1
sudo mount /dev/vol2/p1 /mnt/vol2_p1
sudo fdisk -l
...

Disk /dev/mapper/vol2-p1: 52 MiB, 54525952 bytes, 106496 sectors # ~50M

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

sudo lvs
  LV        VG        Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
  ubuntu-lv ubuntu-vg -wi-ao---- <63.00g
  p1        vol1      -wi-a-----  12.00m
  p1        vol2      -wi-ao----  52.00m
sudo lvresize vol2/p1 --size 70M # raise to 70M

Rounding size to boundary between physical extents: 72.00 MiB.

Size of logical volume vol2/p1 changed from 52.00 MiB (13 extents) to 72.00 MiB (18 extents).

Logical volume vol2/p1 successfully resized.

sudo fdisk -l
...

Disk /dev/mapper/vol2-p1: 72 MiB, 75497472 bytes, 147456 sectors # ~70M

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes