Forefront TMG implements a cache of frequently requested objects to improve the speed of Web access and improve network performance. To enable caching, you must specifically allocate disk space for the cache. By default, after installation, no space is defined for the cache. You can enable caching when you run the Web Access wizard, or you can enable it using the instructions in this topic.
The following procedures describe how to enable caching, and how to configure the way objects are cached and expired objects are served from the cache.
To enable caching
In the Forefront TMG Management console, in the tree, click the Web Access Policy node, and under Related Tasks, click Configure Web Caching.
On the Cache Drives tab, select the server entry, and then click Configure.
Select the required drive, and in Maximum cache size, specify the maximum size in megabytes. Click Set to save the setting. Click Reset to set the value back to 0. The maximum size for a single cache file is 64 GB. If you require a larger cache store, you can split it into several files over different drives.
Note: A cache can only be enabled on a disk drive using the NTFS file system.
To disable caching, set the cache drive size to 0. Check cache rules before disabling caching. Content that is served only from the cache will not be available if caching is disabled.
To configure advanced caching properties, leave the Cache Settings dialog box open, and continue with the next procedure.
To configure how objects are cached and how expired objects are served from the cache
In the Cache Settings dialog box, click the Advanced tab.
Leave the default setting Cache objects that have an unspecified last modification time enabled, to specify that pages, or objects that do not have a time stamp of the last modification, can still be cached.
Leave the default setting Cache object event if they do not have an HTTP status code of 200, to specify that pages without this status code should be cached. The HTTP 200 status code is an OK response to a Web server that indicates that a request is fulfilled, and that a complete page has been obtained.
In Maximum size of URL cached in memory, specify a maximum limit on the size of objects that can be stored in memory. This prevents excessive caching of large objects, such as graphics. A limit that is too low may hinder caching performance, because objects are served more quickly from the memory (RAM) cache.
Select Do not return the expired object (return an error page), to specify that negative caching should not be used. Negative caching allows you to specify the circumstances in which expired cache objects should be returned to users, when a required Web server is not available.
Select Return the expired object only if expiration was, to indicate that in some circumstances, an expired object should be returned. Then select one of the following:
- Select At less that this percentage of
original Time-To-Live, to specify how long an expired object
should be served from the cache, based on a percentage of the
original Time-to-Live (TTL). A TTL value is specified in every
cache rule you create. For example, if you specify a value of 59,
the maximum time period in which the expired object is returned, is
50 percent of the original TTL setting.
- Select But no more than (minutes), to
indicate that an expired object should not be returned if the
expiry time was greater than the specified number of minutes, even
if it falls within the TTL setting specified previously.
- Select At less that this percentage of original Time-To-Live, to specify how long an expired object should be served from the cache, based on a percentage of the original Time-to-Live (TTL). A TTL value is specified in every cache rule you create. For example, if you specify a value of 59, the maximum time period in which the expired object is returned, is 50 percent of the original TTL setting.
In Percentage of free memory to use for caching, specify the percentage of RAM made available for caching. The default is 10 percent.
ConceptsCaching Web site content
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