There’s lots of information around, relating to how to improve VMware performance; some of it useful and some of it not so useful.
For example, it does help to be reminded to defrag your guest OS virtual hard disks – but being told that fibre channel is faster than DAS is a little pointless, when you’re trying to improve the speed of your personal VMware box and don’t have the budget for such things.
So with this in mind, I’ve collected bits and pieces that I have found made a big difference to performance, without having to spend money on hardware.
Firstly, the Guest OS:
1. As mentioned above, where appropriate, always keep the virtual disks de-fragmented.
It does make a small improvement to performance and disk size. Obviously, the more fragmented the disk, the worse the performance and the bigger the file size.
2. Use the minimum number of CPUs per guest OS.
Contrary to “real” computers, more processors does not equal more power. In fact, it can equal less power. If you have a dual or quad core host system, synchronising your cores across the guest OS, with the host OS’s use of them is actually likely to degrade performance, not enhance it. A CPU can only process one thing at a time (albeit pretty damn quickly), so each instruction has to queue and be run in synchronisation. It’s likely that if you try your guest with just one CPU, it will perform better than if you try it with two. Especially if you are using more virtual CPUs than you have physical.
3. Always choose the SCSI disks over the IDE.
As can be seen here, a virtual IDE controller will use more CPU load than a virtual SCSI controller.
4. Always install VMware Tools on the guest OS.
It allows the guest to stay in better communication with the host and will help.
5. Pre-allocate disk space.
It’s faster but it makes the storage requirements more of a problem. Your call.
6. Disable anything you don’t need.
A guest VM does not need visual pretties, high res wallpapers, screensavers, etc. Turn them off. You don’t need a fancy Matrix-style screensaver that requires 40% of the CPU and 512MB of RAM, on a screen no one can even see. Any services you don’t need, as well.
7. No RAID.
There is no sane reason why the guest OS needs virtual disks in a virtual RAID. This makes no sense – they’re almost certainly just files stored on the same physical disk or RAID anyway – let the Host OS worry about RAID.
8. Don’t use Snapshots.
They really slow Guest OS systems down.
Speeding up the Host
There’s only so much you can do on the guest, to make an impact, if the host is running slow. So let’s address what we can, there, as well. You’re likely to find a bigger impact on the Host than the guest.
1. Set up the hard drives in the most efficient, fastest fashion.
Obviously, a slow software RAID is going to degrade performance – but you may not have a choice. I myself use a software RAID-1 on my VMware Host because I am willing to sacrifice some performance for peace of mind and i don’t have the money for a real RAID card – but I acknowledge the performance will be degraded.
2. Don’t over use resources.
You have a finite amount of RAM and number of CPUs. Deal with it. Don’t allocate 10 VM guests, with a CPU and 2GB of RAM each on a dual core PC with 4GB of RAM and then complain things are slow. If you care about performance, then allocate 1 CPU to the Host OS, and 1 CPU per guest. Ensure the Host OS has enough RAM to do its job and don’t allocate more RAM than you have, physically.
3. The Host OS must be minimised.
The Host OS should not need to run a web server, etc, etc. It should be a VMware server. That’s all it should be doing. Don’t install junk you don’t need and, if possible, don’t use Windows as the Host OS. This is because you can squeeze a lot more performance out a Linux host, with a much smaller footprint. You won’t need to run anti-virus products, etc, which all hog memory and CPU cycles.
4. The Host OS should be maximised.
Maximise the performance of the Host OS and the way VMware Server 2.x interacts with it. See below for practical ways to do this, right now, with next to no effort. They make a very noticeable performance.
5. Disable power management on your Host OS.
If you’re running Linux, compile the kernel to use noapic, (you may need to do this anyway, on an AMD chip). See the link (also on this blog) as to how to do this.
6. Synchronise the CPU speed on the Guest and Host systems.
See this entry (on this blog) as to how to do this.
7. Set the Host system BIOS up for maximum performance.
There will almost certainly be an option in your BIOS for maximum performance. Basically, this sets the CPU timer to be constant, not cycling down to conserve heat / power, etc.
8. Separate physical disks for OS and VMware Guests.
This way, the OS read / writes don’t interfere with the VMware guest disk I/O. Obviously, the faster the disks, the better.
9. Make some config changes to your Host VMware Server.
Out of the box, VMware works fine – but performance isn’t great – especially disk I/O. The below changes make significant improvements over default performance.
Changes to the VMware configuration (assuming Linux Host OS).
1. Edit the /etc/vmware/config file. Add the following:
tmpDirectory = "/tmp/vmware"
mainMem.useNamedFile = "FALSE"
sched.mem.pshare.enable = "FALSE"... Read more
MemTrimRate = "0"
MemAllowAutoScaleDown = "FALSE"
prefvmx.useRecommendedLockedMemSize = "TRUE"
prefvmx.minVmMemPct = "100"
Basically, what we’ve done here is set a new temporary directory for VMware to use (we’ll come to this in a minute). Then we’ve told it use no more memory than we actually have and to stop sharing it between guests (much faster), not allow memory trimming and cut out sharing of certain resources.
2. Give VMware it’s own temporary location (swap) for files.
As you see above, we’ve defined a new location for VMware to keep it’s swap info, instead of in the regular file system. Aside from the above, we now need to make a location “/tmp/vmware“. We then create the following entry in /etc/fstab, so we can define this location as new file system:
tmpfs /tmp/vmware tmpfs defaults,size=100% 0 0
Now Linux knows this location is a temporary file system – think of it a bit like a swap file.
Once you make the changes above, you can expect to see a reasonable performance improvement, as opposed to a “vanilla” VMware Server 2.x environment. I can personally attest to a really noticeable disk I/O improvement, especially on Windows based Guest systems.
