Office Web App default cache size is 100 GB

Earlier today I noticed some fairly innocuous commentary in the Features that influence the size of content databases section of the Storage and SQL Server capacity planning and configuration (SharePoint Server 2010) TechNet guidance:

“If Office Web Apps are being used, the Office Web Apps cache can significantly affect the size of a content database. By default, the Office Web Apps cache is configured to be 100 GB. For more information about the size of the Office Web Apps cache, see Manage the Office Web Apps cache.”

100 GB? Surely that can’t be right. So I followed the link and found that:

The Microsoft Word Web App and Microsoft PowerPoint Web App generate a series of images to create a rendition of a document that is viewable in the browser. If Microsoft Silverlight 3 is installed, XAML is used to create the rendition. Creating the rendition can consume large amounts of computer resources. To reduce resource consumption, the Word Web App and PowerPoint Web App store the renditions in a cache, created as part of a SharePoint content database. Renditions in the cache are then used for future requests of a view of the same document. In an environment where most documents change infrequently, but are viewed regularly, maximizing the space dedicated to the cache or the expiration period, can improve performance and reduce resource consumption. In an environment where most documents frequently change, you can optimize performance by reducing the space that is dedicated to the cache, or by reducing the time documents are stored in the cache.

So… make sure to plan SQL database disk space accordingly (nb: this is an update to the original post – I originally thought this was front-end disk space). Also note that you can pin the cache to a specific site collection’s content database. Either reduce the cache size (instructions in that link above) and adjust according to performance needs or invest in SQL storage accordingly.

And don’t forget to plunder the enormous investments Microsoft are making in SharePoint 2010 documentation. It’s the only way you’ll find out about all of these considerations.