Everyone is talking about virtualization these days (Well, all us geeks at least). There is very good reason for it. It can drastically reduce both operating and operational costs, is easy to use and can be very cheap to implement.
After evaluating several option (VM, Xen, Sun, Oracle) we chose a Xen solution from Citrix. Several reasons made us decide on the underdog Xen. The biggest reason of course is price. The base edition of Xen which includes required features for an enterprise implementation such as failover (manual) and snapshotting is free. Along with this, Xen is open source, with this a growing community is adding new feaures and plug-ins for it. Not near the level of VMWare yet, but getting there.
Our Implementation
We implemented Xen by using four Dell R series servers, two switches (Powerconnect 5424) and a MD3000i iSCSI NAS. Total cost for all hardware was VERY cheap.
As per image, we build a XEN pool using the free Citrix Xen software, connected two GBE connections to one 5424 and two to the other for iSCSI (along with two more for LAN). For the MD3000i, each controller has one network to each 5424. The allows full redundancy, maintenance on a server, switch, or the MD will not affect any virtual server guests.
Using this method, we have virtualized over twenty servers onto these four servers with more being added. (Our estimated maximum is 30, and this is due only to the MD3000i) Server include Terminal Services servers, web servers, “legacy” database servers. This is saving us tens of thousand a year in operation support for legacy hardware plus has the added benefit of increasing the servers uptime due to the full redundancy.
Your Implementation
I recommend as a first step building a test environment to play with Xen, iSCSI, converting physical to virtual guests, etc. All you require are two servers (or Desktops) as virtual servers (They require VT chipset,
run this tool to verify), basic switches and a server with some storage as the iSCSI NAS.
Use this guide to build your environment. You can use as the guide specifies, Openfiler as your NAS, or, I recommend
Starwind as your NAS software as there is a free version and it is much easier to use than Openfiler and prone to much less errors.
Key things to remember
- Once you implement Virtualization management believes it is an unlimited pool, where server after server can be added. I often hear “There is no budget for this new project which requires a server, can’t we just virtualize it?” It is a constant effort to educate.
- You will run out of memory resources before CPU. Xen cannot do memory overcommit. This means that if you give a server 8GB of RAM, that RAM cannot be shared and is dedicated to this server. Only allocate as much RAM as a server requires.
- Disk speeds through iSCSI are MUCH slower than physical disks. Using our MD3000i all our guests (Over 20) share the two 1GB network connections to the MD. This means over twenty servers are sharing 2GB disk speeds. One high-utilization database server can kill disk performance for all. if you have a server that requires and uses allot of disk IO do not virtualize!!! (Unless of course you are using 10GBE)
- If you have 3 Virtual Servers, scale the guest size to as if you have two virtual servers. (This is especially key with memory) This allows you to take one server offline for maintenance or any hardware issues. If you do not do this, you lose all redundancy!
- If your server requires any physical devices such as USB, Serial, or PCI device Xen virtual guests cannot access these. These servers are not good candidates for virtualization.
I hope this helps you get your toes wet in virtualization and Xen!
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