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rolionoff
n00b
Joined: 15 Oct 2004
Posts: 6
Location: Switzerland
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 Posted: Thu Sep 29, 2005 1:02 pm Post subject: SOLVED: vserver or UML on Server? |
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I'm planning to setup a server which has the usual things as web-, mailservers and additionally a X server available via Nomachine NX (or VNC).
I can use "unlimited" free IPs as long I have a sufficient reason 
So I want to isolate at least:
- X server
- the rest
The host system will probably be unaltered (SSH only) to make it more secure.
Searching through the forums, I have seen that UML and vserver have their advantages and disadvantages. So is there anybody having a similar setup as I'm planning to build or could you tell me what "virtualizer" you use and the advantages/disadvantages of them?
I'm planning on writing a short overview about the posts, so don't be shy |
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rolionoff
n00b
Joined: 15 Oct 2004
Posts: 6
Location: Switzerland
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| Posted: Sat Oct 01, 2005 11:40 am Post subject: |
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Update:
Main advantage of UML: You can
create a template where you install a base system. Then you make copies with COW (copy on writing) which saves diskspace because the shared components are installed in the template.
Main disadvantage of UML: Every virtual machine uses the same amount of RAM as the host system. Even worser: You have to multiply it by 2 because the host system "mirrors" the RAM which the VM uses  The only way to fix: allocate a fixed amount of RAM to the VM which is smaller than the total RAM of the host system. But this will lead to more swapping from the VM...
Main advantage of vserver: RAM is dynamically allocated, you don't have to waste precious memory
Disadvantage: Disk space cannot be "shared" like in UML.
What I didn't knew was that vserver allocates RAM dynamically, I thought that you have to reserve to every VM a certain amount of RAM. In this case, both options would have been equal - which was the reason why I asked for advice...
But since vserver allocates the RAM dynamically, it's very clear what to choose
Your comments are still welcome.
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Assume Epsilon>0...
At least, honourable mathematicians have found the number Epsilon. It is so small that it becomes negative if one divides it by 2. |
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rolionoff
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Joined: 15 Oct 2004
Posts: 6
Location: Switzerland
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| Posted: Sun Oct 02, 2005 11:09 am Post subject: |
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From http://www.openvps.org/Plone/docs/user/faq/uml
| Quote: | What is the difference between User-Mode Linux (UML) and VServer?
This is bt no means the definitive answer to this question, but it highlights at least some of the significant differences between UML and Linux VServer.
VServer technology is better suited than UML in hosted Virtual Server applications because VServer provides wider resource sharing and practically no overhead therefore minimizing the cost to the provider (meaning that hosting provider can put more accounts on the same box while maintaining decent performance). UML is better suited for situations where isolation is more important than performance, e.g. kernel development and testing.
A VServer-based virtual server will not allow mounting of external filesystems, manipulation of network configuration including routing and filtering (iptables). While a UML-based Virtual Server will functionally appear more like a hardware server, a VServer is going to be much more responsive and will scale higher on the same hardware.
VServer-based virtual servers run in the same kernel as the main system which makes every virtual server "closer to the hardware" and therefore faster. User-Mode Linux runs a separate Linux kernel for every virtual server in user mode. This provides a greater level of abstraction from physical hardware, however it is also considerably more resource intensive.
VServer-based virtual servers have access to all of the physical server memory which is arbitrated and optimized by a single kernel, again, resulting in a considerable performance advantage. UML servers require stringent segmentation of available memory, only limited amount of which can be available to the virtual server. Each UML virtual server manages its own swap, resulting in a considerable extra disk IO and degrading overall disk performance.
VServer shares the same disk partition for all virtual servers, resulting in a more efficient overall disk utilization, and disk space limits can be adjusted on-the-fly without even stopping the virtual server operation. Most providers of UML servers use loop-device mounted fixed-size partitions which makes it difficult to adjust available disk space and also carries some overhead. |
Remember: OpenVPS is based on the same sources as vserver, but not the same... so be careful if you use the tips from openvps.org!
_________________
Assume Epsilon>0...
At least, honourable mathematicians have found the number Epsilon. It is so small that it becomes negative if one divides it by 2. |
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SnarlCat
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Joined: 21 Sep 2005
Posts: 40
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| Posted: Mon Oct 03, 2005 1:24 pm Post subject: Xen |
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If you're on an x86, you may look into the Xen hypervisor.. UML and (I think) Vserver are user-level virtualization techniques; Xen is a kernel-level virtualizer that enforces much greater separation and allows greater performance (fewer context switches, for example)
Pros: mondo performance wrt UML, stability, active development, stable networking, and a Gentoo-Xen howto at http://gentoo-wiki.com/HOWTO_Xen_and_Gentoo to satiate your needs.
Cons: configuration & setup can be tricky (but not so much with the HOWTO from above), no shared disk images (yet)
Hope this helps..
_________________
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Our OS who art in CPU, UNIX be thy name.
Thy programs run, thy syscalls
done, In kernel as it is in user! |
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