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INFO: Proxy Caching Recommendations

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This article applies to:

  • WebMarshal 6.5 and above

Question:

  • What are the best practices for configuration of proxy caching hardware and settings?

Information:

Virus Scanning Exclusion

When setting up proxy caching, you must exclude the cache directory from on-access or resident virus/malware scanning. If WebMarshal determines that the cache directory is being scanned, proxy caching will be disabled. To re-enable caching, correct the scanner exclusions and then restart the WebMarshal Proxy service.

Cache Location

By default the cache directory location is within the WebMarshal install location (on each processing node server). This location is appropriate for trial installations and low volumes of traffic.

However, to ensure adequate performance on production servers, Trustwave recommends you place the cache in another location.

  • Configure the cache on a separate physical disk.
    • Ideally this disk should be used only for the cache.
    • At minimum it should be a different disk to the WebMarshal temp (unpacking) and logging directories.
    • Use a single disk with fast read and seek time. Do not use RAID or mirrored disks (redundancy slows access time). Do not use a compressed disk or folder.
    • Trustwave strongly recommends you use a local disk. The disk must have 100% availability.
      • In 6.5.5 and above you cannot enter a UNC path. (However these versions will use a UNC path if you entered it previously. If you use a UNC path, the Windows account used to run the WebMarshal Proxy service must have full access to the location.)
  • Ensure that the cache disk always has some free space (at least 30% free, and preferably more). Set the cache maximum size accordingly. This will help preserve performance.
  • In an array with more than one processing server, the cache maximum size applies to each server. You can set different maximum sizes for each server using the "server groups" feature in the WebMarshal Console.
  • The cache index is maintained in server memory. If the memory is insufficient, or the cache contains an extremely large number of files, server performance could be slowed due to memory constraints.

Disk Space

  • The default cache size is 10GB. You can set a larger value, but Trustwave recommends a maximum of 20GB. As the cache index is stored in memory, larger cache sizes can use up the available Virtual Address Space for the proxy process (this is a Windows architecture limit).
    • For advanced users who wish to experiment with a larger cache, monitor the Virtual Bytes performance counter for the WebMarshal proxy process to ensure that it is well within the maximum of 2GB at peak load.
  • You should ensure adequate free space will remain on the disk (to allow for disk fragmentation with creation and deletion of many files).
  • The cache maintains a minimum of 1GB free disk space, plus 1MB per GB of configured cache size.
  • If the cache is located on the same disk as the WebMarshal installation, standard WebMarshal low disk space checking also applies. If the disk free space falls below the minimum, browsing requests will be denied.
  • The cache data is not compressed, and you should not use disk compression for the cache disk or folder (this helps to maintain quick access).

Cache Statistics

In addition to the Real-time Dashboard in the Console, you can use the command line WMProxyCacheTool to check and administer the cache. See Knowledge Base article Q12724.

Cache Exclusions

Caching depends on the remote web server to provide correct information about when WebMarshal should retrieve new content. In rare cases, a site may not provide this information. As a result, users may not see the latest content from the site.

If you experience problems with out-of-date content for a specific site or part of a site, you can exclude it from caching. In the WebMarshal Console, see Server and Array Properties > Proxy Cache > Exclusions.


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