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Daniel Nashed

Taking full benefit of RAM for File-System Cache with Domino on W64

Daniel Nashed – 13 March 2014 11:48:59

A long time ago I already blogged about the changes IBM introduced for the file-system cache.
And I ran into this in customer situations many times. I have described it in my IBM Connect session but because I got questions about it again, I think it makes sense to mention it again.

The default settings they implemented might impact you when you add a lot of RAM to your Domino server.

We have seen dramatical reduction of read I/O when adding a lot of RAM to the Windows machine because Windows 64 can leverage the 64bit address space for taking all the remaining memory for file-system case.

But by default there is a very high physical memory limit for the file-system cache.– It will try to use all memory which can cause Domino Memory to be swapped out

On startup of the Domino server the W64 call “SetSystemFileCacheSize()” is used to limit the cache.
Since Domino 8 and higher ships a 64bit helper binary “cacheset.exe” to set the cache size for Domino 32bit. Domino 64bit has this call integrated into the core code.

When the code is executed the system privilege “SE_INCREASE_QUOTA_NAME” is needed (See TN #1391477 for details).

By default the value is set to  30% of memory. That would only work well with a machine with around 8 GB of memory, but even there some tuning might make sense because Domino will usually allocate less than 4 GB of memory.

So you can tune the percentage used via notes.ini MEM_FSCachePercentMem=n
The settings depends on the RAM and the memory that Domino needs in your environment .

Example: 16 GB RAM, 6 GB reserved for Domino/OS = MEM_FSCachePercentMem=65

You can check the current settings with “cacheset.exe -g”
Here is the output from a machine with 8 GB RAM without any settings after the Domino Server has been started once.

cacheset.exe -g
Existing file system cache values are minSizeRead 824488 kb, maxSizeRead 2473264 kb, flags 5

This is really a parameter that you have to look at when you run Domino 32bit/64bit on Windows!

-- Daniel



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