Burstable RAM Memory & VPS Disk I/O
Notice WiredTree claims their lower plan offers "256-MB Guaranteed RAM & 1024-MB Burstable RAM," while their top plan offers: 512-MB Guaranteed RAM and 2048-MB Burstable RAM.
The term Burstable refers to a short-term usage spike, typically not seen in daily monitoring graphs. Any RAM your account does not use is available to be used as burstable memory for other accounts on your physical server (hardware node).
Everything in the world of Virtual Private Servers revolves around memory, but disk input/output is normally the biggest bottleneck (hindrance to server performance) in Virtualized servers. This is because .. well, here's what Zac said:
No virtualization software at this point has a good disk I/O scheduler. Virtuozzo 4 was supposed to have an improved one, but it is pretty much worthless.
We use 8-disk RAID-10 arrays in order to maximize the IOPS (I/O Operations per Second) to minimize the risk that any one VPS can choke disk I/O for the other Virtual Environments.
Virtuozzo, Xen, and other virtualization software are good at scheduling CPU, but weak at scheduling disk I/O. I suppose that will come in time.
If a VPS web host offers burstable limits, that indicates they're using Virtuozzo (virtualization software). Far as I know, none of the hypervisors (either Xen or VMWare) offer burstable memory.
Rather every account on a hypervisor comes with fixed allocations of memory .. which happens to be a major attraction, knowing that no other account can use your memory, and that your host can't allocate part of your memory to another account.
Say, for example, you're paying for a plan that includes 512-MB RAM. And let's say your account begins by using an average of 450-MB. Then one day your account suddenly starts using much less memory (.. say 250-MB). Is this cuz your VPS host re-configured your account to give 200-MB of your memory to another account? (to increase their profit$)?
The downside to hypervisors is that they don't use memory as efficiently as Virtuozzo. Yet some feel this leads to more disk I/O problems (bottlenecks) with Virtuozzo.
On the next page, we'll delve a little deeper into the world of Virtual Private Servers by discussing the differences between Managed and unManaged VPS servers. These options represent the first decision you'll need to make before signing up for your VPS account.
This is where you'll learn you needn't be a Linux admin guru in order to run your own VPS server (as I previously thought).