Parallels VM runs very slow and makes Mac OS run slow

I had a huge problem with my VM (XP Pro) running excruciatingly slowly and making my MacOS (10.4.8) also run very slowly. It's a MacBook Intel Core Duo, 1 GB RAM, 17 GB free HD space. I had the VM set to 604MB memory, per the Parallels recommended max., but finally tried reducing that to 364MB. The performance was vastly improved and became usable! This was very counterintuitive and I didn't find this help in the FAQs or elsewhere in the Parallels site. It always said to not go above the max, but it doesn't say that less is better! So I'm thinking of trying even less, but wondering HOW to determine the optimum and what would be the minimum. Has anyone else had this problem? Thank you.

 

This has been discussed repeatedly on this forum. Your discovery is correct. You should always allocated the MINIMUM amount of RAM to Parallels that provides good performance for YOUR workload. It is impossible to come up with 1 best number, because that number is a function of the apps (both OSX and Windows) that you, your particular machine configuration, and which features of those apps you use the most. The best way to find the right number is through experimentation.

But generally speaking less is more. And if makes perfect sense. The more RAM you allocate to Windows, the less RAM OSX has to run. And since Parallels, and by extension, Windows, are relying on OSX, it makes no sense to starve OSX. Which what you do when you allocate more than 1/2 your physical RAM to your VM.

 

OK, thanks. Another question then, under what keywords can I search to find where this was previously discussed? I searched various versions of "running slow" and came up with nothing. I must not know how to search properly! tks again.

 

It would be very helpful to have some idea what RAM makes sense. For example, with 2GB physical RAM I got much better performance using 512M for Parallels than using 1GB for Parallels. Even with nothing at all running on the Mac side. I would have thought that 1GB for OS X would be enough.

 

OSX is memory hog. The more memory, that happier it is. In addition, if your VM isn't using memory you've allcoated to it, then that memory is wasted, because it could have been used by OSX to cache your VMs disk IO (for instance) but instead is being allocated and unused by the VM.

Here are some rough guidelines:
1. Never alloocate more than 1/2 your physical RAM to Parallels.
2. On machines with 1 G or more (I don't consider 512M machines viable, despte the fact that some people do it successfully) start at 512M. If it's good, lower in 128M increments until performance slows. If performance is poor, raise in 128M increments until performance is good.
3. Do real testing. Don't just change the memory login and open an app and assume that's good. Make a change and use the VM as your would typically for an hour. If all is well, then continue tweaking until you've found your minimum for good performance.

I have 2 G machine and for my XP VM, I use 256M and get great peformance for my uses, which are MS Office (MS Project), GotoMeeting, and web testing using IE and FF on windows.

 

SO, what is the memory recommendation for vista? I had it on 640 MB (2 gig MBP), but i experienced the same issue, OSX was just dragging butt. I did resolve the CPU issue, but now I wonder about the memory starvation issue. I just set it to 512 MB, I'll see if OS X is going to be more responsive....still, any suggestions on the proper memory size for this OS?

D

 

I have your same configuration on a MBB and had 9g HD space left. I was running XPPro SP2 with 604 for menory and OSX dragged horribly, but after reading some of the forums lowered it to 412, which is what Parallels recommended. Both OSes run great. I get the occasional pop-up message that my VM system is low on memory and will increase it (set to Auto in prefs). I use the same apps VTMac does and have 3-4 of them open and they do fine, plus run Safari and iCal on the Mac side. No problem. I have not tried lowering the VM memory anymore.
I made a 10g Boot Camp partition and tried it as a VM but decided I did not need it and got rid of it. I use a firewire drive partition as a shared folder location and it works great. I even ran a VM from the Firewire drive.

C