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YellowSnowIsBad 01-18-2011 02:56 PM

Hardware advice.
Hey, long post, a little unusual so sorry in advance.

just looking for some advice about running several virtual machines on one server, its hardware requirements and what to expect in terms of performance.
since i don't have much experience running such a server, nor with xen hypervisor, i thought i would ask someone who does.

first of all i will explain a little on the uses of machine.
It will run several operating systems through a xen hypervisor. i am a little new to xen and its technologies, but i think i want a hardware assisted virtual environment, one that takes advantage of say amd-v etc.

it will have several machines:

1) the host
2) a router with pfsense
3) a file server, preferably with raid 1
4) a p2p server running mldonkey
5) maybe one machine dedicated to running one or two virtualbox machines. these virtualbox machines will mainly be static, something to play around and target with backtrack, nothing too resource heavy; idle most of the time.
6) a separate vpn machine that can have traffic proxied through it.
7) possibly a separate snort ids machine.

this all sounds pretty demanding, but it will only really serve a small network, one or two machines, both mine.
the three virtual machines that could be considered active and the most resource hungry would be the router, p2p server and possibly the vpn server; although used, they would not be used with insane intensity. the rest would be used reasonably sparingly.

obviously because this will be running my router, amongst other things, i plan to leave it running for some lengths of time, so i thought about some low power cpus.

this one in particular:

i thought about the phenom 955 as it is fast and has l3 cache, but it operates at 125w max. the athlon lacks l3 cache, and for it to handle so many tasks at once, i thought possibly this would affect the latency of traffic traversing my router. think it matters?
i also considered running 4gb of ddr2, say 800mhz simply because of the price. think i should stick to a higher clock ddr3? would 4gb be enough?

over and above all, i was building this machine to get rid of a lot of separate hardware i have running, but i want to make sure that my server can handle several tasks while my router respects low latency for gaming.


genderbender 01-19-2011 06:59 PM

From my experience I've found cpu performance is rarely effected, even with multiple servers. I run a XEN server with 16 VM's on it (Windows and basic proxy servers) and the CPU rarely spikes above 15% (quad core XEON); memory however is the real, major pitfall and drops to the maximum memory usage each time a new VM is added. Take how much memory you'd like to allocate to the VM's and add this together, add another 2GB onto this for the total ammount of memory you'll need to purchase. Also when you set this up don't worry about the memory allocated on XEN center being continually high, this is completely normal, as are CPU spikes when rebooting systems.

The newest xen kernel has support for private network communication (without the need for a physical NIC), XEN also supply free load balancing software which I have some experience with, this would be ideal if something specific ate up your WAN traffic instantly as you could duplicate the VM and add it to your load balancer and split the load, of coure your WAN connection would still be saturated, but it would take the load off the VM's.

I'd have three NIC's: one for your VPN, one for external traffic and one JUST for XEN management (make sure nobody can bypass your router and access this, also prevent remote logins on all your kit and manage it through xen center). When you setup XEN, also setup a private NIC for internal communication which will help with the internal traffic. In terms of CPU speed effecting bandwidth, it wont - unless your routing is tremendiously complicated, you also shouldn't need too much power behind this (my routing boxes have 1CPU and 500MB of memory each), they rarely use any CPU power but seem to hit around 300-400MB of memory. By the way, I wouldnt run virtualbox on top of xen, seems counter intuitive. I also don't see how you can setup a file server as RAID 1 which is virtual, surely the disks of your XEN server will be the only thing using RAID and thus your whole setup will be RAID 1. Oh, that reminds me of my final bit of advice, think carefully about disk space. Like the memory, add the totals together and install a drive with the total. One final thing, XEN can't support file systems over 1TB. If you have 2TB disks, partition them before hand - failing that setup an iscsi type system for data (you can use the internal NIC for this).

Hope that long, verbose reply helps :)

YellowSnowIsBad 01-21-2011 05:45 PM

Thanks, your post answered a lot of questions. Just out of pure interest, what model of xeon processor are you using?

When i said raid 1, i meant a raid 1 pair dedicated for storage for one of the guests. of course, it was a silly question thinking about it now.


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