CentOS - Apr 2021 - Resize a VM: any risk involved ?

Hi,

I'm currently fiddling with KVM, Proxmox and various VMs.

I setup a very basic VM with a manual (fdisk) partitioning scheme: one /boot
partition, one swap partition, and one root partition, the latter being the
last partition and thus expandable).

I'm starting with a reduced disk size (6 GB in total) and a minimal
installation. The idea behind this approach is that I can clone this minimal VM
and then eventually expand it to fit my needs.

Here's how I expand the available disk size.

First I increase the virtual disk in the hypervisor.

Then I fire up the VM and do the following:

# yum install cloud-utils-growpart
# lsblk
# growpart -v /dev/sda 3
# resize2fs /dev/sda3

Now here's my question (finally): is there any risk involved in this sort of
operation? Or can it be performed on a production system without having to
worry about data loss?

Cheers from the sunny South of France,

Niki

-- 
Microlinux - Solutions informatiques durables
7, place de l'?glise - 30730 Montpezat
Site : https://www.microlinux.fr
Blog : https://blog.microlinux.fr
Mail : info at microlinux.fr
T?l. : 04 66 63 10 32
Mob. : 06 51 80 12 12

On 08.04.21 17:43, Nicolas Kovacs wrote:
> Hi,
> 
> I'm currently fiddling with KVM, Proxmox and various VMs.
> 
> I setup a very basic VM with a manual (fdisk) partitioning scheme: one
/boot
> partition, one swap partition, and one root partition, the latter being the
> last partition and thus expandable).
> 
> I'm starting with a reduced disk size (6 GB in total) and a minimal
> installation. The idea behind this approach is that I can clone this
minimal VM
> and then eventually expand it to fit my needs.
> 
> Here's how I expand the available disk size.
> 
> First I increase the virtual disk in the hypervisor.
> 
> Then I fire up the VM and do the following:
> 
> # yum install cloud-utils-growpart
> # lsblk
> # growpart -v /dev/sda 3
> # resize2fs /dev/sda3
> 
> Now here's my question (finally): is there any risk involved in this
sort of
> operation? Or can it be performed on a production system without having to
> worry about data loss?
Just a hint - man virt-resize

--
Leon

> Hi,
>
> I'm currently fiddling with KVM, Proxmox and various VMs.
>
> I setup a very basic VM with a manual (fdisk) partitioning scheme: one
> /boot
> partition, one swap partition, and one root partition, the latter being
> the
> last partition and thus expandable).
>
> I'm starting with a reduced disk size (6 GB in total) and a minimal
> installation. The idea behind this approach is that I can clone this
> minimal VM
> and then eventually expand it to fit my needs.
>
> Here's how I expand the available disk size.
>
> First I increase the virtual disk in the hypervisor.
>
> Then I fire up the VM and do the following:
>
> # yum install cloud-utils-growpart
> # lsblk
> # growpart -v /dev/sda 3
> # resize2fs /dev/sda3
>
> Now here's my question (finally): is there any risk involved in this
sort
> of
> operation? Or can it be performed on a production system without having to
> worry about data loss?
I'm often doing something similar but *not* with partitions. I have either
disk images or logical volumes on the KVM host which I grow and then use
"virsh blockresize" to adjust size. Then on the guest I only have to
resize the filesystem or in case using LVM on the guest, first
"lvextend"
and then resize the filesystem.

Fiddling with partitions without the ability to reboot always scares me a
bit. That's why I prefer not to so it and therefore I have not used
"growpart".

BTW, are you not using XFS these days?

Regards,
Simon

I'm using VirtualBox for a few VMs, the biggest one is a Ubuntu 20.04 that
ocassionally grows too small, so I use virtualbox tools to enlarge the disk
then boot up something that h as gparted in it and use gparted to
stretch/move partitions.

Not being familiar with (i.e., not having used) KVM I can't say what's
the
best way, but it seems to me that gparted would be easier than the steps
you described., once you've changed the partition size.

On Thu, Apr 8, 2021 at 11:43 AM Nicolas Kovacs <info at microlinux.fr>
wrote:
> Hi,
>
> I'm currently fiddling with KVM, Proxmox and various VMs.
>
> I setup a very basic VM with a manual (fdisk) partitioning scheme: one
> /boot
> partition, one swap partition, and one root partition, the latter being the
> last partition and thus expandable).
>
> I'm starting with a reduced disk size (6 GB in total) and a minimal
> installation. The idea behind this approach is that I can clone this
> minimal VM
> and then eventually expand it to fit my needs.
>
> Here's how I expand the available disk size.
>
> First I increase the virtual disk in the hypervisor.
>
> Then I fire up the VM and do the following:
>
> # yum install cloud-utils-growpart
> # lsblk
> # growpart -v /dev/sda 3
> # resize2fs /dev/sda3
>
> Now here's my question (finally): is there any risk involved in this
sort
> of
> operation? Or can it be performed on a production system without having to
> worry about data loss?
>
> Cheers from the sunny South of France,
>
> Niki
>
> --
> Microlinux - Solutions informatiques durables
> 7, place de l'?glise - 30730 Montpezat
> Site : https://www.microlinux.fr
> Blog : https://blog.microlinux.fr
> Mail : info at microlinux.fr
> T?l. : 04 66 63 10 32
> Mob. : 06 51 80 12 12
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> https://lists.centos.org/mailman/listinfo/centos
>

You could make a copy of the VM, and? see if you can resize things? with 
the copy and see if it breaks?

On 4/8/21 9:43 AM, Nicolas Kovacs wrote:
> Hi,
>
> I'm currently fiddling with KVM, Proxmox and various VMs.
>
> I setup a very basic VM with a manual (fdisk) partitioning scheme: one
/boot
> partition, one swap partition, and one root partition, the latter being the
> last partition and thus expandable).
>
> I'm starting with a reduced disk size (6 GB in total) and a minimal
> installation. The idea behind this approach is that I can clone this
minimal VM
> and then eventually expand it to fit my needs.
>
> Here's how I expand the available disk size.
>
> First I increase the virtual disk in the hypervisor.
>
> Then I fire up the VM and do the following:
>
> # yum install cloud-utils-growpart
> # lsblk
> # growpart -v /dev/sda 3
> # resize2fs /dev/sda3
>
> Now here's my question (finally): is there any risk involved in this
sort of
> operation? Or can it be performed on a production system without having to
> worry about data loss?
>
> Cheers from the sunny South of France,
>
> Niki
>

Hi,

    Wow... I didn't know about "growpart" :)

     I do, however, on XenServer (now XCP-NG) almost the same thing for
ages:

     - shutdown the VM
     - increase disk size on XCenter
     - boot VM on maintenance mode (with DVD boot)
     - do fdisk /dev/xvda, remove the desired partition (in your case 3),
and recreate it with the same initial block and occupying the rest of the
disk.
     - make what's is need to use the new space on the partition, in my
case it's a LVM partition used as a PVE block. Than pvresize, vgextend,
etc...

     Until now, no problems...

     Att.,

                Antonio.




Em qui., 8 de abr. de 2021 ?s 12:44, Nicolas Kovacs <info at
microlinux.fr>
escreveu:
> Hi,
>
> I'm currently fiddling with KVM, Proxmox and various VMs.
>
> I setup a very basic VM with a manual (fdisk) partitioning scheme: one
> /boot
> partition, one swap partition, and one root partition, the latter being the
> last partition and thus expandable).
>
> I'm starting with a reduced disk size (6 GB in total) and a minimal
> installation. The idea behind this approach is that I can clone this
> minimal VM
> and then eventually expand it to fit my needs.
>
> Here's how I expand the available disk size.
>
> First I increase the virtual disk in the hypervisor.
>
> Then I fire up the VM and do the following:
>
> # yum install cloud-utils-growpart
> # lsblk
> # growpart -v /dev/sda 3
> # resize2fs /dev/sda3
>
> Now here's my question (finally): is there any risk involved in this
sort
> of
> operation? Or can it be performed on a production system without having to
> worry about data loss?
>
> Cheers from the sunny South of France,
>
> Niki
>
> --
> Microlinux - Solutions informatiques durables
> 7, place de l'?glise - 30730 Montpezat
> Site : https://www.microlinux.fr
> Blog : https://blog.microlinux.fr
> Mail : info at microlinux.fr
> T?l. : 04 66 63 10 32
> Mob. : 06 51 80 12 12
> _______________________________________________
> CentOS mailing list
> CentOS at centos.org
> https://lists.centos.org/mailman/listinfo/centos
>

-- 
*Antonio da Silva Martins Jr. *
*Analista de Suporte*
NPD - N?cleo de Processamento de Dados
UEM - Universidade Estadual de Maring?
email: *asmartins at uem.br* <asmartins at uem.br>
fone: +55 (44) 3011-4015 / 3011-4411
inoc-dba: 263076*100

    "Real Programmers don?t need comments ? the code is obvious."

On 4/8/21 11:43 AM, Nicolas Kovacs wrote:
> # yum install cloud-utils-growpart
> # lsblk
> # growpart -v /dev/sda 3
> # resize2fs /dev/sda3
> 
> Now here's my question (finally): is there any risk involved in this
sort of
> operation? Or can it be performed on a production system without having to
> worry about data loss?
Risk from a Virtual Machine perspective or just generally?  One of the 
many operations I do often with VMs is "mess" with disks treating them
as logical devices means I can add storage later, easy, when needed. In 
most cases I don't take the system down at all. "It just works".

But there are always risks. If you're doing this manually, typos can 
bring down your system. Another part of your risk is using partitions. 
Partions, particular the "system" drive where rootfs is, can act oddly
on Linux when it's live. It's not rare that you find the kernel refusing
to do a "partprobe" on /dev/sda - which means you need a reboot for
the
kernel to see the new size of a partition. Next, your partition stuff is 
very limited - compared to so many other things you have in CentOS you 
should really avoid using partitions for anything - well, perhaps but 
that's about it.

I use LVM on all my systems. To expand a system I simply add a new 
virtual disk, expand the VG, and then expand the filesystem using 
"lvexpand -r". It's painless and there are no risks of conflicts.
LVM
allows me to remove the disk later if need be - ie. the first disk size 
you added was 50GB but you realize a few months later that you 
calculated wrong as should have added 500GB. LVM allows you to add a new 
disk of 500GB, move everything from the old disk to the new, and then 
you can remove the new one - all without taking down the file system!

It also comes with snapshot features for persistent backups. So at a 
risk of sounding like a broken record, don't use partitions. If risk is 
what you're focused on, there's a lot more risk using plain partitions 
vs. volume management.

-- 
Regards
   Peter Larsen