Performance of static vs. expanding images?

Hi All,

when the german PC mag c't reviewed Parallels Desktop for Mac they mentioned a significant performance difference between static and expanding VM images in favor of static VM images. Is it correct that expanding images imply costs in terms of performance drops?

Best regards, Shaun.

 

No one tested that? Really?

 

I'd be very interested to hear about this also.

 

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Yes, static disks are faster.

With the price of storage so moderate, there must only be emotional reasons for using dynamic.
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I wonder if this performance difference is constant, or perhaps only while the disk is growing (such as during installation). E.g. once the disk is no longer growing, is there any performance difference?

 

There are definitely non-emotional reasons to use dynamic if you're using it on a laptop. Laptop drives top out at 160GB. At this time, they don't come any bigger than that. I originally started with 120GB (which is big for a laptop) but quickly ran out of space and had to upgrade my drive to Seagate 160GB just to fit another VM on it. If my laptop VM's were fully expanded to their maximum size, I'd be out of space again.

I agree with you on the desktop. I've got loads of space with the 250GB boot drive and three additional internal 500GB drives.

 

xochi raised a question I was wondering about, too. It is quite logical that dynamic disks are slower than static ones due to all the administration overhead both in Parallels and the host OS when new space needs to be allocated.

However, the rate in which allocations of new space happen will lose momentum over time. Deleting files in the guest OS frees disk space that can be used later to store new data. After sufficient uptime of the guest OS, administration overhead will mostly amount to nothing more than checking if there is sufficient free disk space in the dynamic disk.

I wonder if the Parallels develpment team has tested this.

Bye, Shaun


p.s.: The reason for posting this was the exact point Pleiades is making. On installation of Parallels, I had 80 GB of my 120 notebook drive available. Back then, I found static VMs to be a good idea (speed, speed, speed). Due to heavy mathematical computations with tons of output I now need about 60 GB spare disk space - and would like to try BootCamp, too. So 160 GB are on their way but I'd still like to switch to dynamic VMs to save even more space.

 

I heard a podcast on Security Now where Steve Gibson talks extensively about dynamic vs expanding images and he actuay did some real time experimenting on this subject. I suggest you listen to the full podcast at www.twit.tv and click on the left on Security Now episode 58. He really does a good job of explaining the difference and why each one has its advantages and disadvantages.