fix last PR Vonng#166, fix redundant spaces in references in ch1.md also

ch1.md

@@ -107,9 +107,9 @@
 
 我们通常认为硬件故障是随机的、相互独立的：一台机器的磁盘失效并不意味着另一台机器的磁盘也会失效。大量硬件组件不可能同时发生故障，除非它们存在比较弱的相关性（同样的原因导致关联性错误，例如服务器机架的温度）。
 
-另一类错误是内部的**系统性错误（systematic error）**【8】。这类错误难以预料，而且因为是跨节点相关的，所以比起不相关的硬件故障往往可能造成更多的**系统失效**【9】。例子包括：
+另一类错误是内部的**系统性错误（systematic error）**【8】。这类错误难以预料，而且因为是跨节点相关的，所以比起不相关的硬件故障往往可能造成更多的**系统失效**【5】。例子包括：
 
-* 接受特定的错误输入，便导致所有应用服务器实例崩溃的BUG。例如2012年6月30日的闰秒，由于Linux内核中的一个错误，许多应用同时挂掉了。
+* 接受特定的错误输入，便导致所有应用服务器实例崩溃的BUG。例如2012年6月30日的闰秒，由于Linux内核中的一个错误【9】，许多应用同时挂掉了。
 * 失控进程会用尽一些共享资源，包括CPU时间、内存、磁盘空间或网络带宽。
 * 系统依赖的服务变慢，没有响应，或者开始返回错误的响应。
 * 级联故障，一个组件中的小故障触发另一个组件中的故障，进而触发更多的故障【10】。
@@ -378,12 +378,12 @@
 1.  Brian Beach: “[Hard Drive Reliability Update – Sep 2014](https://www.backblaze.com/blog/hard-drive-reliability-update-september-2014/),” *backblaze.com*, September 23, 2014.
 1.  Laurie Voss: “[AWS: The Good, the Bad and the Ugly](https://web.archive.org/web/20160429075023/http://blog.awe.sm/2012/12/18/aws-the-good-the-bad-and-the-ugly/),” *blog.awe.sm*, December 18, 2012.
 1.  Haryadi S. Gunawi, Mingzhe Hao, Tanakorn Leesatapornwongsa, et al.: “[What Bugs Live in the Cloud?](http://ucare.cs.uchicago.edu/pdf/socc14-cbs.pdf),” at *5th ACM Symposium on Cloud Computing* (SoCC), November 2014. [doi:10.1145/2670979.2670986](http://dx.doi.org/10.1145/2670979.2670986)
-1.  Nelson Minar:  “[Leap Second Crashes Half   the Internet](http://www.somebits.com/weblog/tech/bad/leap-second-2012.html),” *somebits.com*, July 3, 2012.
-1.  Amazon Web Services:  “[Summary of the Amazon EC2 and Amazon RDS Service   Disruption in the US East Region](http://aws.amazon.com/message/65648/),” *aws.amazon.com*, April 29, 2011.
+1.  Nelson Minar:  “[Leap Second Crashes Half the Internet](http://www.somebits.com/weblog/tech/bad/leap-second-2012.html),” *somebits.com*, July 3, 2012.
+1.  Amazon Web Services:  “[Summary of the Amazon EC2 and Amazon RDS Service Disruption in the US East Region](http://aws.amazon.com/message/65648/),” *aws.amazon.com*, April 29, 2011.
 1.  Richard I. Cook: “[How Complex Systems Fail](http://web.mit.edu/2.75/resources/random/How%20Complex%20Systems%20Fail.pdf),” Cognitive Technologies Laboratory, April 2000.
 1.  Jay Kreps: “[Getting Real About Distributed System Reliability](http://blog.empathybox.com/post/19574936361/getting-real-about-distributed-system-reliability),” *blog.empathybox.com*, March 19, 2012.
 1.  David Oppenheimer, Archana Ganapathi, and David A. Patterson: “[Why Do Internet Services Fail, and What Can Be Done About It?](http://static.usenix.org/legacy/events/usits03/tech/full_papers/oppenheimer/oppenheimer.pdf),” at *4th USENIX Symposium on Internet Technologies and Systems* (USITS), March 2003.
-1.  Nathan Marz:  “[Principles   of Software Engineering, Part 1](http://nathanmarz.com/blog/principles-of-software-engineering-part-1.html),” *nathanmarz.com*, April 2, 2013.
+1.  Nathan Marz:  “[Principles of Software Engineering, Part 1](http://nathanmarz.com/blog/principles-of-software-engineering-part-1.html),” *nathanmarz.com*, April 2, 2013.
 1.  Michael Jurewitz:“[The Human Impact of Bugs](http://jury.me/blog/2013/3/14/the-human-impact-of-bugs),” *jury.me*, March 15, 2013.
 1.  Raffi Krikorian: “[Timelines at Scale](http://www.infoq.com/presentations/Twitter-Timeline-Scalability),” at *QCon San Francisco*, November 2012.
 1.  Martin Fowler: *Patterns of Enterprise Application Architecture*. Addison Wesley, 2002. ISBN: 978-0-321-12742-6