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High memory VM's
Which hypervisor (Xen, KVM, or OpenVZ), would be best to handle a situation where you have:
A smaller number of VM's (say max 8) and each VM is allocated 6-8G of RAM each. Then each VM for example decides to use most of their allocated RAM, thereby coming close to reaching full capacity of RAM on the host.
Or does it not really matter?
Comments
For high memory VM's I'd probably stay away from Openvz, but either Xen or KVM would be fine. You'd probably be better also offering XEN-HVM so that they'd be more like semi-dedicated servers than VPS.
Why would you stay away from OpenVZ? All can be oversold.
I imagine OpenVZ would be the best because there's less overhead. It depends what you plan on using the VPSes for, since memory allocation is weird on the .18 kernels.
@DanielM
Probably because how stupid OpenVZ handles memory.
We've never had a single issue with OpenVZ besides it not allowing all memory to be used, but that was patched in a kernel update a few days after ErrantWeb opened in January. OpenVZ is really criticized as a oversold option. However no one seems to want to see about the provider, and see how it runs. I know for a fact our nodes run fine. People use us for Minecraft ( something that other providers here that run openvz say wont work correctly on openvz ). OpenVZ is a great option for anything unless you need to run your own kernel.
Errant,
The problem is historically its been used for overselling and still can to this day. That is not to say people do not run it correctly.
I would say KVM as you can over allocate RAM if you need to
@ErrantWeb my biggest complaint with non-vswap openvz is things like this:
################################################################################## # Misconfigured mysql and I ended up with a container "using" (allocating) 431MB # # more memory than the host's memory usage including buffers and caches # ################################################################################## [root@claw ~]# vzlist CTID NPROC STATUS IP_ADDR HOSTNAME 110 15 running 192.168.1.206 vps-110.claw.local 111 12 running 192.168.1.207 vps-111.claw.local 112 12 running 192.168.1.208 vps-112.claw.local [root@claw ~]# free -m total used free shared buffers cached Mem: 746 143 602 0 0 22 -/+ buffers/cache: 120 625 Swap: 1503 0 1503 [root@claw ~]# vzctl enter 110 entered into CT 110 [root@vps-110 /]# free -m total used free shared buffers cached Mem: 746 574 171 0 0 0 -/+ buffers/cache: 574 171 Swap: 0 0 0 ############################################################################## # Later, I was playing with Apache 2.4, and the default config resulted in a # # container "using" more memory than the host had # ############################################################################## [root@vz ~]# free -m total used free shared buffers cached Mem: 755 322 433 0 16 207 -/+ buffers/cache: 97 657 Swap: 0 0 0 [root@vz ~]# vzctl exec 206 free -m total used free shared buffers cached Mem: 755 755 0 0 0 0 -/+ buffers/cache: 755 0 Swap: 0 0 0 [root@vz ~]# vzlist CTID NPROC STATUS IP_ADDR HOSTNAME 205 12 running 192.168.1.205 test128 206 94 running 192.168.1.206 httpd2.4.test /proc/user_beancounters showed 857.6 MB had been allocated.No, Minecraft works fine if you set the Java machine's memory limits when you execute the jar file. It should work fine with all OpenVZ setups, assuming there's enough memory to run it.
The way I understood it KVM/Xen cannot be oversold. They can be "ballooned" or some such, but that requires the cooperation of the kernel, so its in your control.