Virtual CPU allocation

[gmizzle]

I plan to use our RHEL6 server as a host for three virtual database servers.

When allocating CPU and memory, how much do I need to retain for the the host?

[Irithori]

No idea.
I guess, you are the best to tell
As you know the setup and applications you intend to use.


In general:
Virtualization and databases dont mix so well,
as DBs usually need any performance they can get.

That said, for a test or development setup it might be sufficient.

[Rubberman]

Assuming that these aren't enterprise class databases, but are relatively small and not performance critical (see Irithori's comment), then it depends upon what load the host will be handling, aside from the virtual machines. In my case, I typically allocate 1 CPU/Core per VM, and 1-2GB of RAM. I have an 8-core 3GHz system w/ 8GB of RAM and don't run more than 2 VM's at a time on it, especially since it is also my development workstation. FWIW, disc I/O is the biggest Linux performance hog. The latest kernel has done a lot, from what I hear, to help deal with that as far as impact upon front-end processes, but since I am still running a CentOS 5 system (same as RHEL 5), that doesn't help me a lot.

So, three virtual DB servers? You should have a 4-8 core host w/ 8-16GB of RAM, and put the virtual disc images on separate host drives if you can. Ditto for disc controllers, though that is sometimes difficult. Do make sure they are not on your drive that has your host system swap and other system space.

[mieropj]

Hi,

For the host, 512 MB will be OK. Usually, the host does not run applications except some small ones to control the VM servers hosted.
Give the remaining memory to hosts !

Cheers,
JJ