服务器2008 R2和分支缓存

文件缓存的概念已经存在很多年了。事实上，这是IBM使其PS/2 Model 50电脑比其前身IBM AT表现更好的方法之一，尽管AT的硬盘实际上比PS/2的硬盘更快。今天的计算平台在许多不同的层次上使用缓存。文件系统缓存在驱动器控制器的硬件中，然后再由操作系统缓存在内存中;缓存MAC和DNS地址;内存缓存在微处理器上;网页文件被浏览器缓存;这样的例子不胜枚举。Server 2008 R2中的BranchCache特性是缓存概念的一个大规模“宏”应用。其思想是，通过慢速和/或断断续续的广域网路链接将分公司与公司总部分隔开，分公司应该缓存用户请求的文件内容，这样将来就不必通过广域网路来检索相同的内容。 To use this feature, you must be running Server 2008 R2 on the file servers or Web servers whose content is to be cached, and Windows 7 on the client systems in the branch office. If you decide to cache content in the branch office on a server instead of on clients, then that server, too, must be running Server 2008 R2. The two modes of operation are “distributed” mode and “hosted” mode. In distributed mode, which to me is (at least conceptually) far less desirable, the Windows 7 clients do the initial caching of requested data, and they also do the sharing of that data to other Windows 7 clients making subsequent requests for the same content. Distributed mode can only work across one subnet in the branch location and it obviously breaks down when clients containing cached content go to sleep or are powered down. “Hosted” mode uses a server (which does not have to be dedicated to the caching function) to act as the file cache. Windows 7 clients requesting data from a central office get identifiers instead of actual data, then the clients check with the BranchCache server to see if the data is there from a previous lookup. If not, the client gets the actual data from the central office, and subsequently provides the data to the BranchCache server for storage, in the hope that some other Windows 7 client will need the same data later. Will this mechanism actually improve file retrieval performance? It will depend on a lot of factors, not least of which is the degree to which the exchange of identifiers can occur quickly and efficiently. There’s also the bandwidth available in the WAN link, and probably most important, the frequency with which multiple users in a branch need the same content from the central office. With a high percentage of unique data requests, BranchCache might not provide much of a boost, and could conceivably even slow things down. However, the principle of data caching is time-tested. For branch offices that do a lot of repetitive content retrieval, it might be worth a try – as soon as you’re running Windows 7 on all your clients.