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I've noticed our 'dedicated' web server is running on an MS VM. I don't like it, cause we can't tell if another VM is running on the same machine or not, other than taking the word of the provider.

But my question is; can it still be called a dedicated server if it's just a single VM on a server?

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up vote 3 down vote accepted

It is an accurate but imprecise use of the word. That VM is dedicated to your use so it is a dedicated virtual machine in that sense.

It is usually assumed that dedicated means all the hardware associated with the machine is dedicated to you, which is not the case here: you are sharing CPU resources and I/O bandwidth (and depending on host setup, memory allocation). We have a specific term for this L: the Virtual Private Server or Virtual Dedicated Server (VPS or VDS, the latter term used to be more common but has pretty much fallen out of use).

IMO you could definitely make a case for calling a VM a dedicated server as a deliberate attempt to mislead/mis-sell unless:

  • it is the only VM running on the host. This is sometimes done when you want to dedicate a machine to a task that is CPU/IO/... intensive but you also want some of the conveniences of virtual environments like being able to flip back and forth between snapshots, or having a consistent set of hardware even if the host underneath changes significantly. There is still some performance hit from using the virtualisation layer, but the hit is predictable as there are no other VMs or major tasks on the host to content with for resources.
  • OR you have truly dedicated resources on the host:
    • truly dedicated RAM that is fixed in physical memory (the host not being permitted to swap the stuff out, in fact not permitted to swap other tasks out either as that would likely impact your VM too)
    • truly dedicated storage: your VM is on its own physical drive that is not otherwise used by the host or other VMs
    • a fixed number of CPU cores and a guarantee that no more or assigned that exist (i.e. on an 8 core machine nor more than seven are assigned to VMs leaving a bit of CPU for the hosts jiggery pokery) - even this is not the same as having truly dedicated hardware but is probably close enough
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Actually one hoster promotes "single virtual image servers" for easys of update / replacement and the snapshot thing. Get your own VM on your own hardware. – TomTom Jan 24 '12 at 12:06
Nicely examined, David. Indeed I'm trying to figure out if a single VPS on a host could be called a dedicated server or would it be more of a VPS. And can we tell in the company meeting, it's not really a dedicated hosting as it was advertised. Considering all opinions, I think we can tell it's more of a VPS. – SuperDuck Jan 24 '12 at 13:43

Google define for dedicated:

(of a thing) Exclusively allocated to or intended for a particular service or purpose.

The service specification you agreed upon with your provider should tell you if having a VM is "dedicated" or not. But basically, you should not care - what you should care about is performance. As long as it works out for you, it does not matter if the system is virtualized or not - consider it as a management or hardware abstraction tool employed by your provider.

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Thanks for the definiton. You are right about the part, in general it's the performance what matters. But I'm trying to decide if we can tell it's not really a dedicated hosting, but a VPS in our company meeting. – SuperDuck Jan 24 '12 at 13:30

Technically it can. I mean, you can call anything anything, certainly in sales-terminology. Doesn't mean it's true though.

Feels a little misleading because of the IO overhead of virtualisation.

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Which is close to 0 - the IO overhead. SO not relevant. – TomTom Jan 24 '12 at 11:22
Yes yes, It could run on your phone(!) – Tom O'Connor Jan 24 '12 at 11:38
The I/O overhead is not close to zero if the virtual drives are using allocate-on-write storage: there is a measurable difference in performance here both for each I/O operation and due to fragmentation (the VM may think its filesystem is completely fragment free but the file hosting it could be a complete mess - what should be sequential I/O becomes much more random). The biggest I/O hit for VMs though is from other VMs (and the host) if this VM is not the only thing actively doing something significant in that regard. – David Spillett Jan 24 '12 at 11:57
But all that is can be handled with a proper IO subsystem. FOr example my main virtualization server has 8 velociraptors as RAID 10 for it's virtualsation discs. Soon with a SSD read/write cache. No server comes close to the IO capability. for root discs. SO the overhead is negative here. – TomTom Jan 24 '12 at 12:05
Thanks for your opinions Tom. Basically you are right and that's also what I think. I find 'a little misleading' a good definiton. I'm trying to decide if we can tell it's not really a dedicated hosting in our objection at the company meeting. – SuperDuck Jan 24 '12 at 13:26

In webhosting you install multiple webservers on one host which is most of the time virtual. So you have multiple hosts with multiple webservers on one physical machine.

What you have is one of the virtual hosts on the physical machine. This VM is under your full control and no one else has access to it. You can install software on it, manage user access, control the firewall settings and so on. Which means it is dedicated. So I guess there are more VMs on the physical machine.

If there would be just one VM on one server, I think it would be a waste of resources. Also it would have been simpler just to install the OS directly on the physical machine without a hypervisor inbetween.

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Thanks for sharing Tom. Well we could call all VPS services 'dedicated', but they are more of a 'dedicated VM', or VPS. I was actually trying to find the border between dedicated and VPS services, for in-house discussions. – SuperDuck Jan 24 '12 at 13:18

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