I just recently built a new Q6600 rig and I am running Ubuntu 7.10 64-bit and VMware v6.0.2 build-59824 on it. I run 2 separate WinXP 32-bit VM's on this machine (one for work & one for play ;))...
And I've been hearing thru a number of different sources (googling, and [URL="http://communities.v
Meaning it's better to run a VM with 1 core instead of 2, and less then 1000mb of ram :confused:
This is a very difficult for me to get my head wrapped around because I am new to virtualization, and I've always just run a XP rig natively where more = better, more cores, more ram = better performance, why is this not the case for VirtualMachines?
I just don't get it :confused:
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Couldn't find the one on VMware's site anymore (??) but there is a rundown at the virtual memory link listed below.
from http://wiki.novell.com/ind
This memory section is faster and more efficient. Bear this in mind with your VM guests - try to plan around using less than 896MB RAM to keep your guests running optimally. (with a link to http://linux-mm.org/Virtua
Some considerations with memory explained in this techpaper:
http://www.vmware.com/supp
Maybe that is what they are refering to when talking about keeping it under 1 gig.
At that point you can try testing it out on your own. If your guest needs the 8gb of RAM go for it, but I've never seen an app that does (I live in the 32bit realm these days)
I can tell you on a number of apps I tested, 896 was far better than 1.5gigs. Try it out - run some benchmarks - and see for yourself.
It has to do with how memory is accessed. I don't claim to understand a lot of the technical details listed on that linux-mm page, but it seems to hold true.
I believe this memory discussion is flawed for several reasons:
1. The HOST is running Linux so you would need to keep the VMWorkstation App running in the first X megabytes of memory but since your HOST has 8 Gigs of memory you can't controle which code is in which memory segment.
2. The GUEST is Windows XP and when you give it not enough memory it will start swapping more to disk which is I/O and thus much more costly than any overhead incurred by memory paging on the CPU.
If we were talking about VMWare ESX server things might be a bit different because ESX uses an install on the bare metal of a modified Linux kernel. With VMware workstation you effectively run everything in user process memory space and have up to 4 Gb of address space according to the linux-mm page.
Also see this guide:
http://www.vmware.com/pdf/
"On the one hand, you should allocate enough memory to hold the working set of applications you will
run in the virtual machine. On the other hand, unlike native systems, on which more physical memory is almost always better, allocating too much virtual memory to a virtual machine can reduce overall system performance, and can even reduce the performance of the overallocated virtual machine. This is because allocating to a virtual machine much more memory than its working set requires can increase memory pressure at the host level (as the host balances VMware Workstations memory requests against the systems other memory needs)."
Also, since VMware's hosted products are using mmap for allocating memory, keeping the amount of memory allocated to the VMs down to a level where they get what they need (and then some) will give you better performance.
Halindar: ESX'es vmkernel is not a "modified Linux kernel". Some ESX versions however ship with a Service Console VM based on RHEL3.
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by: HalindarPosted on 2008-03-14 at 13:24:20ID: 21129160
On the core issue:
What you need to keep in mind is that a virtual machine with two virtual cores running on a two core host can only get pocessor time on that host if both host cores are available. While a single core VM only needs to have one of the two host cores available. Now if you are running a 2V-Core and two 1V-core VMs on a 2 core host your 1V-core VMs will statistically get more time on the host CPU cores because if either one of the 1V-core VMs has a claim the 2V-core VM can't use the remaining host core.
So unless your VM hosts an application that can take extra benifts from having 2 cores (parralell processing) like MS SQL 2005 then you're better of useing 1V-core VMs
As for the RAM, it depends on how much memory your VM typically needs. If you allocate more memory then it actually needs that memory under VMWare server will not be available for the other VMs. Also if your host starts running low on memory it will swap to disk which will impact performance so you need to make sure there is enough memory left for your host to function ok.
Personally with memory I have yet to see demonstrated that less = more unless the host OS has not enough memory remaining.