如果有多个磁盘，那么把负载分配到不同的磁盘上是加快读写速度的有效方法，因为磁盘延迟的最大组成部分是寻道时间。
If you have several disks, splitting load onto separate spindles is an effective way of making reads and writes faster because the largest component of disk latency is the seek time.
数据传输时间一般几毫秒，所以旋转延迟时间和寻道时间是一个物理hdd的主要磁盘延迟时间来源。
Data transfer times are typically fractions of a millisecond, so rotational latency and seek time are the primary sources of disk latency on a physical HDD.
当应用程序发出磁盘请求的速率快于磁盘返回数据的速率时，操作系统会让磁盘请求排队，还可能调整请求的次序以降低寻道时间。
The operating system queues disk requests when the applications issue them faster than the disks can return the data, optionally reordering them to minimize seeking.
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