Understanding I/O【每日一译】--2013-01-07

The performance of many software applications is inherently limited by disk I/O.
Applications that spend the majority of CPU time waiting for I/O activity to complete

are said to be I/O-bound.

非常多的软件应用的性能天性限制于磁盘I/O.应用花用主要的CPU时间来等待IO活动的完成，

我们称作为I/O限制。

Oracle is designed so that if an application is well written, its performance should not
be limited by I/O. Tuning I/O can enhance the performance of the application if the
I/O system is operating at or near capacity and is not able to service the I/O requests
within an acceptable time. However, tuning I/O cannot help performance if the
application is not I/O-bound (for example, when CPU is the limiting factor).

Consider the following database requirements when designing an I/O system:

O是被用来设计的，所以如果应用有好的写的能力，它的性能将不会限制于I/O。调试I/O可以

增强应用的性能如果IO系统正操作在或者接近在它的吞吐量的附近，并且它的服务不能在一个

IO要求的可接受的时间内。不过有时调试IO不能帮助解决性能问题如果应用不是因为IO的限制

（比如，当CPU是限制因素时）。

确定以下几种几种数据库要求当设计一个IO系统时：

■ Storage, such as minimum disk capacity
■ Availability, such as continuous (24 x 7) or business hours only
■ Performance, such as I/O throughput and application response times
Many I/O designs plan for storage and availability requirements with the assumption
that performance will not be an issue. This is not always the case. Optimally, the
number of disks and controllers to be configured should be determined by I/O
throughput and redundancy requirements. Then, the size of disks can be determined

by the storage requirements.

#存储，比如最小化磁盘容量

#可用性，比如连续的（24*7）或者仅在商业时间限制

#性能，比如IO的吞吐量和应用的反应时间

非常多的IO设计计划对于存储和高用性的要求都是在假定性能不是问题的情况下。当然也

不是一直是这种情况。最佳方案是，磁盘的数量和控制器的配置取决于IO的吞吐量和冗余的

要求 。那么，磁盘的大小取决于存储的要求。