KVM vs OpenVZ 7

nullroute · April 2020

I searched the internet for information about KVM and OpenVZ 7. Each site has a different opinion. I would really like to know the real differences, advantages and benefits of each type of virtualization.

WSS · April 2020

KVM is a full system emulation. You can run anything on it.

OpenVZ is a Linux kernel only abstraction, and, whatever. I feel that it is shitty due to shared ports across the whole box, and several other reasons, but that's why I hate it as an admin. For basic stuff, it works perfectly fine, and generally costs less because it can be completely overloaded.

Do whatcha gonna do.

seriesn · April 2020

@nullroute said:
I searched the internet for information about KVM and OpenVZ 7. Each site has a different opinion. I would really like to know the real differences, advantages and benefits of each type of virtualization.

I will try to make it as simple as possible,

I have 0 experience with vz7 maybe @AnthonySmith can share some insight. But based of OpenVZ6/LXC or anything based off of container system, ovz vps is essentially a glorified shared hosting. Imagine a shared hosting, add root login + basic customization. Essentially if your computer is the host node, your different users are your VPS. (not the most technically correct answers but that is the easiest way I can explain it).

KVM - A small computer. You can do anything and everything you want to, you have full control over encrypting your disk, load your own module, tweaking kernel and some more.

nullroute · April 2020

@seriesn said:

@nullroute said:
I searched the internet for information about KVM and OpenVZ 7. Each site has a different opinion. I would really like to know the real differences, advantages and benefits of each type of virtualization.

I will try to make it as simple as possible,

I have 0 experience with vz7 maybe @AnthonySmith can share some insight. But based of OpenVZ6/LXC or anything based off of container system, ovz vps is essentially a glorified shared hosting. Imagine a shared hosting, add root login + basic customization. Essentially if your computer is the host node, your different users are your VPS. (not the most technically correct answers but that is the easiest way I can explain it).

KVM - A small computer. You can do anything and everything you want to, you have full control over encrypting your disk, load your own module, tweaking kernel and some more.

Excellent explanation, in terms of performance with several containers, which one does better?

InceptionHosting · April 2020

One is full virt, the other is a container, the differences are vast yet the end results for end users can be the same.

VZ5/6/7/LXC are containers you share the kernel with the host node but by share I don't mean you have any access to it you just get what you are given in terms of features/capabilities etc.

KVM is more like a tiny dedicated server.

Both however it should be said are shared resource environments in terms of ram/disk/cpu/network.

VZ on simfs used to be faster than KVM in terms of disk back in the vz5 early vz6 days but that is no longer the case.

In terms of which does better, it depends on the environment and use case, you can save a LOT of ram using VZ as you don't have kernel overhead (directly)

VZ7 is a bit of a different animal to 6, unfortunately in solusvm v1 at least VZ7 has just been made to function like VZ6 which is a real shame as it has some pretty significant improvements and features such as built in clustering, OS deployment using EZ templates which allow full automation and package level selection in advance of deployment and live migrations.

Virtualizor have done the worst job of supporting it you could imagine.

I hope when solus.io supports containers they take advantage of its benefits.

From a hosting perspective VZ7 does not have the same density levels of VZ6 but it still is significantly better than KVM (unsurprisingly) which comes to the cost element, it will always be cheaper for a host to offer VZ than KVM.

So if you want to do something that does not involve complex networking, does not require kernel level tuning or modifications in most cases VZ is fine, if you want to optimize and have no restrictions at all then KVM is your choice.

I would say these days it is less of a glorified shared hosting plan which is certainly was when VZ5 was around and simfs was the filesystem for VZ, VZ7 is essentially virtualization but not full virt and with a shares kernel, much liek DO/Vultr when they first launched and ran a shared kernel system on KVM (crazy kids).

mikho · April 2020

@AnthonySmith said: Virtualizor have done the worst job of supporting it you could imagine.

+++100000 on this

@AnthonySmith said: From a hosting perspective VZ7 does not have the same density levels of VZ6 but it still is significantly better than KVM (unsurprisingly) which comes to the cost element, it will always be cheaper for a host to offer VZ than KVM.

On some, not all, nodes of mine, I can see less RAM usage (highly unprofessional opinion, approx the same amount of containers running random stuff).

nullroute · April 2020

After some time of in-depth research, my decision was KVM. My most sincere opinion about OpenVZ is that only obscure and overselling providers use it. KVM is much more complete, safe and stable, its prediction is long years against OpenVZ which may die soon.

InceptionHosting · April 2020

@nullroute said: My most sincere opinion about OpenVZ is that only obscure and overselling providers use it.

Sorry for being obscure

@nullroute said: OpenVZ which may die soon

Highly unlikely, let me give you an example.

Ubuntu 20.

Needs 512MB Ram just to boot on KVM, 1GB to be worth using, everything will be in the same position within a few years.

On VZ it needs a couple of mb to boot and runs at about 9mb ram used when started.

VPS node with 64GB Ram.

KVM = guaranteed that around half the Ram will be used just by the running OS's even if idle , as such my density goes down your prices go up, you only want a VPN.

VZ7 = about 1% of the Ram is used just by the running OS's even if idle so my density goes up, that means I can almost half my prices for you, as TUN works fine and you only wanted a VPN why pay more?

There are probably another 100 use cases but really the bottom line is, VZ has a market, a healthy one, it is pointless turning it in to some north vz south style battle, the evidence over the last 10 years speaks for itself, price is king and KVM is simply more expensive.

nullroute · April 2020

@AnthonySmith said:

@nullroute said: My most sincere opinion about OpenVZ is that only obscure and overselling providers use it.

Sorry for being obscure

I forgive you, but just this once.

cybertech · April 2020

@AnthonySmith said:

@nullroute said: My most sincere opinion about OpenVZ is that only obscure and overselling providers use it.

Sorry for being obscure

@nullroute said: OpenVZ which may die soon

Highly unlikely, let me give you an example.

Ubuntu 20.

Needs 512MB Ram just to boot on KVM, 1GB to be worth using, everything will be in the same position within a few years.

On VZ it needs a couple of mb to boot and runs at about 9mb ram used when started.

VPS node with 64GB Ram.

KVM = guaranteed that around half the Ram will be used just by the running OS's even if idle , as such my density goes down your prices go up, you only want a VPN.

VZ7 = about 1% of the Ram is used just by the running OS's even if idle so my density goes up, that means I can almost half my prices for you, as TUN works fine and you only wanted a VPN why pay more?

There are probably another 100 use cases but really the bottom line is, VZ has a market, a healthy one, it is pointless turning it in to some north vz south style battle, the evidence over the last 10 years speaks for itself, price is king and KVM is simply more expensive.

Download more ram!

mikho · April 2020

@nullroute said:
After some time of in-depth research, my decision was KVM. My most sincere opinion about OpenVZ is that only obscure and overselling providers use it.

Guilty as charged.

@nullroute said:

KVM is much more complete, safe and stable, its prediction is long years against OpenVZ which may die soon.

don't think OpenVZ will die soon, my guess would be around the time when CC implements ipv6.

WSS · April 2020

The biggest problem with OVZ is that all patches are third party and not mainstream, where KVM is part of the kernel. If Virtuozzo becomes insolvent, OVZ7 will go the same way as OVZ6 with even less support.

elliotc · April 2020

I basically only buy KVM products now. Hardware becomes much cheaper than in the past. IP itself is "costly", More memory isn't much more expensive. I instead think what heavy oversold on OpenVZ is the hard drive rather than ram.

nullroute · April 2020

@elliotc said:
I basically only buy KVM products now. Hardware becomes much cheaper than in the past. IP itself is "costly", More memory isn't much more expensive. I instead think what heavy oversold on OpenVZ is the hard drive rather than ram.

RAM is over-sold on OpenVZ, disk and network are always over-sold regardless of the type of virtualization.

Not_Oles · April 2020

@AnthonySmith said: DO/Vultr when they first launched and ran a shared kernel system on KVM (crazy kids)

DO/Vultr were running a shared kernel system on KVM. A quick Google search didn't get me much either on the concept of a shared kernel on KVM or on the fact that DO/Vultr were doing this. Can anybody please point me at more information on either the concept or the fact, or both? Thanks!

FlamingSpaceJunk · April 2020

@Not_Oles said:
DO/Vultr were running a shared kernel system on KVM. A quick Google search didn't get me much either on the concept of a shared kernel on KVM or on the fact that DO/Vultr were doing this. Can anybody please point me at more information on either the concept or the fact, or both? Thanks!

KVM can directly boot a kernel. This might be what they did. I've seen the option, but I haven't tried it.

QEMU/KVM can do some wild stuff, and I use like 10% of its functionality.

SagnikS · April 2020

@nullroute said: disk and network are always over-sold regardless of the type of virtualization

I don't think most providers would oversell disk space, esp on KVM, as it's dangerous potentially. Network is shared on a fair share basis however.

vpsgeek3333 · April 2020

@SagnikS said:

@nullroute said: disk and network are always over-sold regardless of the type of virtualization

I don't think most providers would oversell disk space, esp on KVM, as it's dangerous potentially. Network is shared on a fair share basis however.

It isn't dangerous when you use Qcow2, Raw or thin_lv instead of plain old LVM. Virtualizor & SolusVM both support thin provisioning. Overselling disk space on KVM is a very common practice but yes it needs to be monitored more because the used disk space expands when usage increases but doesn't shrink when usage decreases. I have subscribed 5+ TB where total Disk space available is 2 TB to a few friends. Total disk space usage has reached 34% in 5 years. This is KVM 1.5.x on CentOS 7 with qcow2. And yes I did it because I knew they are never going to use that much space

InceptionHosting · April 2020

The issue with LVM + KVM is that it bottle necks NVMe, not that because you use thin/raw you have to oversell though.

SagnikS · April 2020

@vpsgeek3333 said:
It isn't dangerous when you use Qcow2, Raw or thin_lv instead of plain old LVM. Virtualizor & SolusVM both support thin provisioning. Overselling disk space on KVM is a very common practice but yes it needs to be monitored more because the used disk space expands when usage increases but doesn't shrink when usage decreases. I have subscribed 5+ TB where total Disk space available is 2 TB to a few friends. Total disk space usage has reached 34% in 5 years. This is KVM 1.5.x on CentOS 7 with qcow2. And yes I did it because I knew they are never going to use that much space

It's probably okay if you do it for friends, but in a production environment, I really don't feel confident. If all the available disk space is used up, it might cause filesystem inconsistencies, and might corrupt data. Not really sure how it's handled actually, however. I've just read it on various docs that your data might get corrupted.
I use Proxmox w/ raw and discard is on, for selling VMs, and most full nudes are under 50% usage.
On a side note, is this how most providers offer a pretty decent chunk of SSD/NVMe space, per GB RAM?

comi · April 2020

@SagnikS said: and most full nudes are under 50% usage.

subscribed!

SagnikS · April 2020

@comi said:

@SagnikS said: and most full nudes are under 50% usage.

subscribed!

Ah crap, can't even edit now.

HostMayo · April 2020

Why not install virtualizor and you can offer both using multivert. To me openvz is a much better option as it uses less overheads (already described above in detail) and its more easily manageable from the control panel as the openvz vps is very much tight to the kernel of master server. But KVM is getting more in demand now days as many of the clients argue that their script only works on KVM. I also found that CloudLinux has limited their support for openvz. So in the end I would suggest to go for multivert as it will enable you to sell off more from the dedi.

WSS · April 2020

You are aware that you can run OpenVZ in a KVM service, but not a functional KVM in an OpenVZ, right?

vpsgeek3333 · April 2020

@SagnikS said:
On a side note, is this how most providers offer a pretty decent chunk of SSD/NVMe space, per GB RAM?

yeap

vpsgeek3333 · April 2020

@WSS said:
You are aware that you can run OpenVZ in a KVM service, but not a functional KVM in an OpenVZ, right?

I remember many hosts used to do slabbing back when OpenVZ was the most popular thing as they always had same nodes going down at same time

comi · May 2020

@Billa said: But KVM is getting more in demand now days as many of the clients argue that their script only works on KVM.

I almost always look for KVM because I pay yearly and I don't know in advance what I will be using it for. Maybe I will need it maybe I won't.

Just imagine debugging a script which works fine on your computer, but not on your customer's server then finding out that it will start working as soon as you do modprobe cool_mod and the server is OVZ...

Scripts where invented to glue stuff together and stuff can have arbitrary needs.

If I know for a fact I wont need "kernel access", that's another story. For example my storage VPS is OpenVZ, everything else - KVM.

KVM vs OpenVZ 7

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