SQL Server 2005 的scalability到底是指什么？

以前对数据库了解的并不多，最近由于项目的需要，看了一些SQL   Server   2005的资料，大多数很模糊，我想请高手指点一下scalability到底是指什么？

具体来说，我们的项目中使用了一台DB   Server，可是随着数据的不断增多而且有大量的应用需要访问数据，DB   Server   就变成了bottleneck，我想请问，有没有这样的scalability，就是如果一台DB   成为了bottleneck，就再加一台DB，如果后来又不够用，就再添加一台，有点像分步式DB，这么多DB共同实现负载均衡，处理来自应用的请求。我不知道这样的情况是不是可能实现，听起来有点像天方夜谭，毕竟DB之间的同步，事务处理，数据的分割都非常困难。听一些同事说Oracle   10g可以支持这样的应用模式，但SQL   Server不可以。

就我看的资料来看，SQL   Server   2005   的新特征，什么database   mirror，failover   clustering，基本上都是HA方面的，难道这就是MS所说的scalability？

请熟悉的人指点一下。

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关注。
可能是没多少人在大项目占使用sql server 的原因，估计对这样的问题知道答案的人也不多。
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database mirror，failover clustering
实现的是高可用性, 即保证服务不会中止, 当一台服务器死掉的时候, 另一台服务器可以接过来继续工作

database mirror 是数据库级的配置, 不是硬件级的(除非你把需要至少两台服务器看作一个硬件级的实现)
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SQL Server 2005 extended the horizontal partitioning concept, by allowing placing partitions of the same table within a single database. In order to fully realize performance and scalability advantages, such partitions should be assigned to separate filegroups based on appropriately defined criteria, which are established by partitioning functions and associated partitioning schemes.

The partition function determines the distribution of rows of a table or index across partitions and is applied by comparing its formula against values in a designated column (called the partitioning column).

A partitioning scheme assigns each of the partitions to a specific filegroup. Note that in order to maximize performance and scalability benefits it is important to both properly select the partitioning column and define the partitioning function associated with it. The choice should depend on data distribution and the type of activities that are typically performed against the target table. For example, if data is used to produce monthly reports, then partitioning based on the date column using monthly intervals as partition boundaries would be a very likely candidate.