Home / server / Questions / 1132399
Accepted
motorbass
Asked: 2023-06-01 21:41:15 +0800 CST

Differences between sfdisk and fdisk on LVM disk extend

  • 772

In order to semi-automate LVM partitions extend on Debian 11 VMs clones from a template, I feel a bit stuck when I try to script it through sfdisk compared to interactive fdisk.

  1. Here's the original partitionning
root# sudo fdisk /dev/sda

Commande (m pour l'aide) : p
Disque /dev/sda : 45 GiB, 48318382080 octets, 94371840 secteurs
Modèle de disque : VDISK
Unités : secteur de 1 × 512 = 512 octets
Taille de secteur (logique / physique) : 512 octets / 4096 octets
taille d'E/S (minimale / optimale) : 4096 octets / 1048576 octets
Type d'étiquette de disque : dos
Identifiant de disque : 0x919d40af

Périphérique Amorçage    Début      Fin Secteurs Taille Id Type
/dev/sda1    *            2048  2000895  1998848   976M 83 Linux
/dev/sda2              2000896 86962175 84961280  40,5G 8e LVM Linux
/dev/sda3             86964222 94369791  7405570   3,5G  5 Étendue
/dev/sda5             86964224 94369791  7405568   3,5G 83 Linux
  1. I perform the following tasks through fdisk to extend LVM's VGs : Note: sda3 and sda5 aren't used, that's why i delete them.
  • delete partition 5 : "d", 5
  • delete partition 3 : "d", 3
  • delete partition 2 : "d", 2
  • create new extended part 2 with default start/end sectors and type is LVM: "n", "e", "2", "t", "lvm"

the result is :

Commande (m pour l'aide) : p
Disque /dev/sda : 45 GiB, 48318382080 octets, 94371840 secteurs
Modèle de disque : VDISK
Unités : secteur de 1 × 512 = 512 octets
Taille de secteur (logique / physique) : 512 octets / 4096 octets
taille d'E/S (minimale / optimale) : 4096 octets / 1048576 octets
Type d'étiquette de disque : dos
Identifiant de disque : 0x919d40af

Périphérique Amorçage   Début      Fin Secteurs Taille Id Type
/dev/sda1    *           2048  2000895  1998848   976M 83 Linux
/dev/sda2             2000896 94371839 92370944    44G 8e LVM Linux

Next, after a VM disk grow from 45=>60GB, i'm able to refresh sda2 with sudo pvresize /dev/sda2

Then, extend my LVM's VGs with sudo lvextend -L +5G /dev/vg/my_vg_name

Finally, resize file system with sudo resize2fs /dev/vg/my_vg_name and successfully reboot.

  1. I want to script those actions (with human validation requirement for sure) so my first idea was to go with sfdisk. Before put the command into a script, i test them manually so i'll do :
  • delete partition 5 : sudo sfdisk /dev/sda 5 --delete --force --lock;
  • delete partition 3 : sudo sfdisk /dev/sda 3 --delete --force --lock;
  • delete partition 2 : sudo sfdisk /dev/sda 2 --delete --force --lock;
  • create new extended part 2 with default start/end sectors and type is LVM:
sudo sfdisk /dev/sda 2 --force --lock << EOF
,,V
write
EOF

Result seems good, sda2 size grew from 45 to ~60GB :

Disque /dev/sda : 60 GiB, 64424509440 octets, 125829120 secteurs
Modèle de disque : VDISK
Unités : secteur de 1 × 512 = 512 octets
Taille de secteur (logique / physique) : 512 octets / 4096 octets
taille d'E/S (minimale / optimale) : 4096 octets / 1048576 octets
Type d'étiquette de disque : dos
Identifiant de disque : 0x919d40af

Périphérique Amorçage   Début       Fin  Secteurs Taille Id Type
/dev/sda1    *           2048   2000895   1998848   976M 83 Linux
/dev/sda2             2000896 125829119 123828224    59G 8e LVM Linux

Now let's refresh sda2 then extend one VG and it goes bad :

root# sudo pvresize /dev/sda2
  Physical volume "/dev/sda2" changed
  1 physical volume(s) resized or updated / 0 physical volume(s) not resized

root# sudo lvextend -L +5G /dev/vg/var
  Insufficient free space: 1280 extents needed, but only 0 available

It seems that partition table isn't up to date with sfdisk whereas it is with fdisk.

Is it a "normal" behaviour of sfdisk or do i missed something there ?

Also, if you have easier ideas or any advices, feel free to tell it if it's constructive.

debian

1 Answers

  1. Best Answer

    Someone from another forum found the solution i'll sum up below: It seems that sfdisk need an explicit partprobe or kpartx -uv /dev/sda after writing changes.

    It means I have to perform the following tasks :

    • Rewrite sda 2 with new size as usual
    sudo sfdisk /dev/sda 2 --force --lock << EOF
,,V
write
EOF
    • then "refresh" sda2
    sudo pvresize /dev/sda2
    • finally launch a partprobe
    sudo partprobe

    Now i'm able to extend and resize my LVM part with

    sudo lvextend -L +5G /dev/vg/var
    • 0