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The Voice of the DBA

Steve Jones is the editor of SQLServerCentral.com and visits a wide variety of data related topics in his daily editorial. Steve has spent years working as a DBA and general purpose Windows administrator, primarily working with SQL Server since it was ported from Sybase in 1990. You can follow Steve on Twitter at twitter.com/way0utwest

SQL Server Thumbnail Metrics – OS Memory

I’m gathering a few metrics around the Internet for SQL Server from people that I think really know how to run a SQL Server. This is a series of posts that I’m making to gather these metrics up for easy access later.

Host Memory

The short metric is:

Leave 4GB for the OS, or 10% of physical (or guest) memory, whichever is greater.

Examples: If I have the following amounts of RAM, I leave this for the OS.

  • 16GB of RAM – leave 4GB since 4 > (16 * 10%)
  • 32GB – leave 4GB since 4 > (32 * 10%)
  • 64GB – leave 6.4GB since (64 * 10%) > 4

Essentially leave 4GB until you get to 48GB of RAM, then go to 10%.

References: Mr. Brent Ozar of Brent Ozar, PLF who’s presented and written this a few times, but the reference I’m using is: How to Set SQL Server Max Memory for VMware

Explanation: In the older x86 days there were all sorts of rules for setting memory for the OS and SQL Server. I won’t go into those, and for the time being we’re working in the x64 world, not x128. For that, you need to be sure the OS isn’t starved by SQL Server and unable to manage the host processes. These days 32GB isn’t expensive, and 4GB gives you a nice cushion at lower levels. At higher ones, you need


Filed under: Blog Tagged: configuration, metrics, sql server, syndicated

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