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It means there is no true definition. Also KVM slices have dedicated resources but they may be less than you hoped for. E.g. a 1GB BuyVM slice has dedicated cpu amounting to 1/8th of a core (do the math, it runs in a 4-core machine with 32gb of ram). But it would be a much less useful VM if it were restricted to that, and in practice you can use 100% of a core on it, as long as not too many users try to do that simultaneously. But if you do that too much, you do get restricted to the guaranteed amount.
Whether that fits the usual concept of overselling depends on your interpretation. I'd say slices work great if your requirements are intermittent or bursty. If you want nonstop dedicated resources, get a dedicated server.
Semi-dedicated is an old hosting term used in early 2000. It basically means less accounts will be hosted on a server for higher performance.
KVM can definitely be oversold / shared, you can oversell CPU, RAM (albeit with some limitations), HDD and network.
For example, let's say a provider has a server with 8 physical cores, puts 30 VPS with 4 cores each on this machine and relies on the fact that most users will use below 20% of the CPU on average, while kicking heavy (ab)users out. This is how a lot of hosting companies operate.
Some providers guarantee you can use all allocated resources, as described, 100% of the time. Even if you mined bitcoin on the machine, the provider wouldn't care as you are not impacting other customers - the processing power is yours, unshared. 1 vCPU = 1 physical thread.
There are no clear definitions on this, as basically everyone makes their own terms - BuyVM calls it "KVM Slices", I call it "Semi-dedicated KVM", Prometeus calls it "LPAR KVM", ServerMania calls it "Hybrid Servers".
Why "semi-dedicated"? I don't think calling a virtual server "dedicated" would be right - a dedicated server is an unshared physical piece of hardware.
TL;DR; Semi-dedicated = VPS with dedicated, unshared CPU power
This has been a good discussion with a lot of insight. I appreciate the feedback.
The term existed when VPS tech wasn't even there. It was either shared or dedicated.
The need for something inbetween was there and semi-dedicated was born. I myself had few semi-dedicated shared hosting back then. I was told only four shared accounts were present on my server.
So for the end user, is XEN better than KVM? Why did XEN "die out"? Was it lack of development or bc it was harder/impossible to oversell?
It's still around and works fine. KVM has become more popular due to technical advantages that I don't completely understand, but either way they aren't overwhelming. They're enough to tip the balance but it's not as if Xen is otherwise unviable.
From the end user perspective, there is no difference between KVM and Xen.
I think that KVM is much easier for a host to setup and maintain minimizing issues and complexity when those arise, than handling a xen infrastructure. But as @FHR said, for the end user, there is no difference in reality.
@caniac22 Now, the "semi" term could mean a lot of different things for each provider, so, you should ask any one individually if you want to know what they do offer as semi dedicated resources. Best of practice, though, for a provider is to state clearly what does he mean in his TOS/AUP or in specs when he is selling the vps.
P.S. KVM and XEN can be oversell, just a little harder than good ol' OVZ
I propose that you ask this question to the operator and wait for a response with detailed clarification what do they mean by this term.
As others have indicated it's not a well defined term and you need to clarify specifically what the provider means where they are using it.
I appreciate it everyone. I'm not in the market for another idle vps but I've seen the term floating around and wondered exactly what it meant. Even after this thread there is no clear definition but at least there's a better understanding.
Semi-dedicated sounds a bit misleading to me. Noisy neighbors on the same physical server can degrade performance for everyone.
I wish people would stop with this overselling debate nonsense. You can have 1GB of RAM and 100GB swap file and oversell the hell out of KVM. You can use OVZ hardware much more efficiently and therefore have many more users on an OVZ server. End users would not experience any symptoms of overselling.
So equating certain virtualization technologies to overselling always has and probably always will be silly.
Yes but less users usually means less probability to have noisy neighbors.