The Update Accelerator caches files (usually updates) from download sites automatically after they are first requested. All subsequent download requests for these files will served by IPFire and processed at local network speed.
Even though the standard Web Proxy cache does almost the same job, there are important differences between the Web Proxy cache and the Update Accelerator cache.
Squid caches the most recently requested data, Update Accelerator caches dedicated software packages.
For example, it would be difficult to reliably store a Service Pack with a size of about 300MB in the Web Proxy cache. Unlike a Web Proxy with its internal cache and uncontrollable results, the Update Accelerator works more as a File Server - the content defined by download usage on the LAN.
The processing can be described as follows. A client on the local network requests a file per HTTP. This request is served by Squid, the web proxy. Squid first redirects this request to his "helpers" (URLFilter, Update Accelerator, Squid Clamav). These modules check whether the request should be processed by themselves. If not, the request is processed by Squid.
In case of Update Accelerator the request is matched against a set of URLs describing possible download sources. If the request matches the process searches the repository for the file and checks whether it is up-to-date. If the file exists and is not outdated, the request URL is rewritten by a URL pointing to the update repository. Thus the request is finally served by the web server of IPFire. Otherwise a download of the file is started to be stored in the repository, the URL is left unchanged.
This behaviour has a little withdrawal: The first download of a file is done twice. One download for the repository, one download for the requester. After storage to the repository each further request is served by IPFire.
Enable log: Update Accelerator logs it's activities to /var/log/updatexlrator
Enable passive mode: If enabled no new downloads are started. Requests are served from the existing update accelerator repository (if the file exists and is not outdated). If you are using the Update Accelerator for the first time you do not want to enable this.
Max. disk usage: Update Accelerator does not start new downloads, if the usage of the file system which holds the repository exceeds this limit. (Default 75%)