FlusiFan

Dimmdrive vs. Windows Disk Cache

2 posts in this topic

Hello Tim,

 

I did some research on RamDisk tools recently and found your product Dimmdrive as an alternative.

However, while I have seen your videos and the access times look quite impressive at first sight, there are some points that I cannot really believe.

 

First of all, Windows has its own Disk or Page Cache located in memory. If a system has enough memory to include the running program executable and the required libraries (e.g. for a game) and additionally a Dimmdrive Ramdisk executable including all of the game file contents, then all this should equally well fit in memory including a Windows Disk Cache with the files even without Dimmdrive add-on.

 

The only difference I can think of is that of course Dimmdrive needs to copy the files from disk to ramdrive first - in other words, it does a prefetch reading all the files before you start your measurements for startup times of a game.

 

If the standard Windows system is given the same chance, i.e. prefetching using a simple program that just recursively open-read-close all the files in the game directory hierarchy from harddisk without copying them anywhere, then the files should as well reside in Windows disk cache and their should be no difference in access and game startup times compared to a ramdisk like Dimmdrive.

 

Of course one could also run the game from harddisk at least one or two times, before performing another measurement and then take only the last duration values as comparison values of Harddisk vs Dimmdrive.

 

If their are still advantages for Dimmdrive, then I believe this might be due to a limited configuration of the Windows Disk Cache (e.g. if the disk cache is configured to max. 128 MB, it can of course not hold 4 GB of files). However, this configuration can most likely be tweaked using some tools.

 

Could you please state the prerequisites and conditions under which your harddisk comparison values have been measured?

Has there been prefetching for the HD test?

How large was the Windows disk cache configuration?

 

The traditional advantages of a ramdisk are that the user can exactly decide what is located in memory - as files are not removed from ramdisk acting as cache if the system needs memory for other purposes. And additionally all write access goes to RAM as well, and is not going directly to harddisk, which speeds up access (e.g. for video work).

 

However in your gaming use-case, these points do not apply, as you in most cases assume that there is enough memory for all of it; there is no other meaningful system activity with exception of the game, and there is nearly no write activity with exception of the savegames.

 

Certainly, if there is not enough memory to hold all the files, the traditional Windows disk cache does not allow to specify which information should be cached as it can be done in Dimmdrive. On the other hand, if somebody just wants to run such a game, it will still work without special configuration with some drawbacks.

 

I admit that Dimmdrive has an easy-to-use interface as there is no need for manually copying files as with other ramdisks. Provided of course, that all the files are located in a directory hierarchy starting at the location of the executable (or its starting directory). I still do not know how it could work, if some executable is used that resides at a different location in the filesystem and / or possibly gets the other files location through some entry stored in registry.

 

BTW: I am just a private person (developer) not involved into any Ramdisk like development. I wrote this just out of interest, just purchased a new rig with 32 GB RAM and want to make the best out of it.

 

Looking forward for your comments.

Michaelnap likes this

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Some good questions!

 

Firstly, for all testing, I completely disable Windows prefetch/superfetch/caching.   This ensures the benchmarks and real-world testing are legit.

 

Secondly, Windows caching works in a way that is very less specific than a ramdisk of any fashion.  They really aren't comparable at all which is why the market for ramdisks exists in the first place.  With Dimmdrive you can ramdrive specific files and be 100% those exist in RAM.  You cannot do that with Windows.  In addition, Dimmdrive syncs files (saves back to HD) if so enabled in real-time, integrates with Steam, and more.

 

The bottom line is usability and a gamer's real-world enjoyment of their game.  Set aside all aspects of everything, playing a demanding game on Dimmdrive is ridiculously faster than playing without.  I like to use Skyrim as an example.  Users are reporting 5-6 times faster in-game transitions (eg, loading a dungeon, etc) with Dimmdrive, which is a massive improvement to the immersive fun quality of playing the game.  

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