I need somebody who knows about virtualisation
If I run htop from my NJ Linode, I see 4 CPUs. Magic. If I run htop on my new UK Tagadab VPS, I see one. I used to have another VPS with another random company and I saw 8 CPUs.
I might be looking at this like a typical middle-manager ("bigger number is better, right?") but surely having access to more than one processor at a time is going to help apps that multi-thread (database mainly), no?
So I sent them an email telling them all this and their chap sent this back today:
> Hi Oli,
Hi there. I just bought a VPS package and I notice that I only have
access to one CPU thread.
>
I've dealt with several other XEN hosting services and have always had
access to at least 4 cores, sometimes 8.
This means that they are probly not ring-fencing the CPU resources very
carfully.
The VPS host has 8 cores in total, and 16G of RAM. Your 512M VPS should
therefore have 1/32nd of the total CPU resources if all VMs on the host
are running high-cpu tasks. In fact you get 1/32nd ring-fenced for your
VM but you can use up to 1/8th (one full core) if other VMs are not
using it. (The actual average CPS usage on our hosts is normally less
than 5%).
This is important because since our VMs allow full root access we
frequently see 'spinning' processes - software written by or installed
by customers which hits an infinite loop and just munches CPU forever.
If we allowed burst CPU across all 8 cores you might find your VM
fighting for CPU resources more often than it currently does.
If you need more CPU resources than a single core can offer then I
suggest moving to a dedicated server where of course you can have as
many cores as you need.
Now I don't know the guts of how XEN splits resources down. No idea at all. That's why I'm a customer… But if I'm theoretically getting unsecure access here or shoddy performance there, I'd like to know.
If a Linoder knows their setup is secure and you think that a 1-core limit would harm my performance, could you give me something I could reply with?
1 Reply
Using their numbers, 32 VPS's sharing 8 cores:
They apparently give each VPS one CPU shared four ways.
If you had 4 cores exposed per VPS, they would each would get four cores shared sixteen ways.
Either way you get the same guaranteed CPU share, but with more cores you can theoretically burst to a higher overall share. If you assume that the other VPS's are normally idle, then more CPU's is better for you.
EDIT:
I would however agree with the last statement they made: > If you need more CPU resources than a single core can offer then I
suggest moving to a dedicated server Busting is nice, but if you are depending on it then you will get burned sooner or later.