performance

This is post #3 in my December-long series on Linux VM performance tuning, Tuningmas. Many system administrators don’t realize it, but in most OSes RAM that’s unused by applications goes towards filesystem cache, which speeds disk operations. Some VM “right-sizing” tools don’t take this into account, and recommend pretty tight memory allocations which end up causing more disk I/O in the long term. Trading some RAM for better I/O performance is often a very good move, both for an individual VM and for the virtual environment as a whole. To understand what’s happening on a Linux VM and make a decision about how much RAM we should leave for filesystem cache we need to understand the ‘free’ command: total used …

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This is post #2 in my December-long series on Linux VM performance tuning, Tuningmas. I remember an old story about people having performance issues on their Windows servers. It would happen intermittently, and never when the system administrator was around. Turns out it was the pretty OpenGL screensaver, which would kick in and slow everything down tremendously. When the admin was around he’d be using the console of the server, so no screen saver, and no problems. Graphical user interfaces make one-off administration tasks easier in some cases, but for virtual environments they come at a cost: additional RAM and CPU overhead. For a virtual environment you should shut them off, or install as little of them as you need, …

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