Matt Ayres on 21 Jun 2008 13:23:51 -0700

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Re: [PLUG] Why Virtualize?

Casey Bralla wrote:
> I've been thinking about virtualizing on servers.  Although I know that 
> virtualized servers are the "next big thing", I can't for the life of me 
> figure out the advantage for virtualizing servers, except for a few very 
> narrowly specific situations.  
There are quite a few reasons to virtualize everything.  I'm not going 
to go by your points, but rather create my own.

1. Using a full hypervisor based system you can consolidate legacy 
servers of any OS.  This means you can buy a new beefy server and 
migrate your  FreeBSD/Linux/Windows/Solaris/etc systems on to that new 
efficient system.  Hypervisor overhead is typically <8% and varies 
depending on the number of virtual machines being run.  Examples: Xen, 
VMWare, Parallels Server
2. You can use OS container virtualization where the hosts kernel is 
virtualized, but limits you to only the OS of the host kernel.  Overhead 
for this type of virtualization is <1% overhead.  This is useful for 
running your Linux/Windows applications and the very low overhead begs 
the question -- Why NOT virtualize?  Using this type of virtualization 
you can easily update for kernel bugs/exploits (benefit of the shared 
kernel), perform mass commands/upgrades inside all virtual machines, 
quickly scale, etc.  Management of hundreds of servers is simplified to 
the same work as only managing a few servers. Examples: Virtuozzo (Linux 
& Windows), OpenVZ (Linux), and Linux VServer.
3. There are other benefits that don't immediately jump out to those new 
to virtualization.  For example backup procedures and management is MUCH 
easier when you're backing up a virtual machine unlike traditional 
backup methods which require a special client installed.  Another huge 
benefit is migration -- using any of the technologies listed you can 
perform live migrations that result in maybe a few TCP packets being 
lost.  Imagine the benefits of this when performing work on a server or 
if you want to balance the load across servers.  The hypervisor systems 
require shared storage (aka. SAN) for this, the Virtuozzo/OpenVZ 
approach does not.

There are still a whole lot more benefits, but these are kind of the big 
selling points.


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