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We have a few SQL Servers with 32 GB or RAM. I've been told that Windows needs a considerable amount of free memory to manage all that RAM efficiently and that I should configure the memory usage on my SQL Server instances to leave around a GB of memory free per 8 GB of RAM, so on a server with 32 GB of RAM and I single SQL Server instance I should configure the instance to use a maximum of 28 GB of RAM.

On the other hand, I've been told that you should not limit the memory a SQL Server instance can use on a dedicated SQL Server.

So, can someone settle this for me once and for all :-)

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You should always limit the amount of RAM that SQL Server can use, otherwise the SQL Server won't leave any RAM for the OS.

You'll usually want to leave 1-2 Gigs of RAM for the OS and the other software on the machine.

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So you think 2 GB is plenty for Windows 2003 regardless of how much RAM it has? This was my thinking until I was told otherwise, but I couldn't see Windows using that much RAM just to manage more RAM. –  Jim Clark Aug 26 '09 at 10:12
    
It "should" be ok. You'll want to monitor the server after SQL has taken all the RAM, and adjust SQL accordingly. It will take a while for SQL Server to release RAM if you configure it on the fly, but it will release the RAM back to the OS if you decide that the OS needs more RAM. It all depends on what is installed on the server besides SQL as to how much RAM you need. If you have backup software installed, it'll need RAM, anti-virus, it'll need RAM, etc. –  mrdenny Aug 26 '09 at 13:31

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