Second web cache for St Andrews
Because of the success of the St Andrews web cache in terms of reducing our network load and budget we have decided to install a second web cache to provide increased performance and resiliency.
The current cache has been operating very well under the current load and needed more disk space to cope with the future volume of traffic as more and more users use the cache. And, because it was in use 24 hours a day, 365 days a year, it was difficult to update the operating system and applications. So we added another cache.
The new cache is based on the Sun Solaris/SPARC platform and has about 8Gb of disk space available for cached files. The new machine is a Sun Ultra 10 with 128Mb RAM and a 300Mhz UltraSPARC IIi processor coupled with a PCI-66 bus and a dual channel SCSI controller which provides approximately twice as much throughput as the equivalent PC-based platform.
The caching software has also been updated to Squid v2.2 which is far more scalable and provides additional features such as Cache Digest (an efficient way of exchanging information between caches) and better monitoring and control interfaces. Also included is the ability to go directly to a web site rather than using the upstream caches, which has improved access to certain licensed sites.
The two caches are now operating in what is known as a sibling relationship - they communicate between themselves to determine which machine has a file before sending the request upstream. And, in order to increase efficiency, we are using a technique called 'URL hashing' which means that for a particular web site everybody sends the request to the same cache server. This means that we only store one copy of the cached files on our servers.
The good news is that those of you who have been using the autoconfiguration option of your web browsers will have been using the new cache automatically - nothing further needs to be done. If your browser supports this feature then we recommend using it - further details are available at:
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