正在寻找一种在外部硬盘驱动器上安装和运行OS X的方法？(OS X)由于几个不同的原因，这可能很有用。首先，它允许您运行另一个OS X(OS X)副本，而无需任何额外的Mac 计算机(Mac computer)。
此外，由于您可以在外部驱动器上运行OS X(OS X)的完整副本，因此它可以用于在其他Mac(Macs)上进行故障排除，也可以作为一种虚拟OS X。我已经写过如何安装OS X在VMware Fusion中，但这会占用Mac上的空间。使用外部驱动器可以节省Mac上的空间，但如果使用USB 2.0可能会慢一些。
在本文中，我将向您介绍将OS X安装到外部硬盘驱动器的要求和步骤。
格式化外接硬盘
您需要做的第一件事是正确格式化外部硬盘驱动器。文件格式(file format)必须是Mac OS X Journaled(Mac OS X Journaled)并且您必须使用GUID 分区(GUID partition)图。为此，请打开磁盘工具(Disk Utility)并将驱动器连接到您的 Mac。
在左侧菜单中的“(hand menu)外部(External)”下，单击您的外部硬盘驱动器，然后单击“擦除(Erase)”按钮。确保在擦除驱动器之前备份所有数据。当您单击Erase时，将弹出一个对话框，您可以在其中配置一些选项。
为您的驱动器命名，为Format选择OS X Extended (Journaled)，为Scheme选择(Scheme)GUID Partition(GUID Partition Ma) Map 。擦除和重新格式化驱动器只需要一两分钟。现在您的驱动器已准备好用于OS(OS X) X。
安装 OS X
有两种方法可以将OS X安装到外部硬盘上：从OS X Utilities 修复屏幕重新安装(OS X Utilities repair)OS X ，或者从App Store下载OS X并运行安装程序。我将向您展示这两种方法，以防其中一种(case one)方法不适合您。
最简单的方法是从App Store下载OS(OS X) X。打开App Store后，您会在右侧看到最新版本的OS X的链接（撰写本文时为El Capitan）。
继续并单击“下载(Download)”按钮开始下载安装程序。请注意，如果您已经安装了该版本的OS X，您会看到弹出消息询问您是否仍要继续。只需点击(Just click) 继续(Continue)。
下载后，只需双击位于Applications文件夹中的安装程序。
继续点击许可协议(license agreement)等，直到出现询问您在哪个磁盘上安装OS X的屏幕。默认情况下，它设置为MacBook。
单击Show All Disks按钮，您将看到Mac上不同磁盘和分区的图标。我将我的外置硬盘命名为OS X，它出现在中间。
您还可以判断它是外部硬盘，因为它使用带有橙色硬盘驱动器的图标。单击(Click) 继续(Continue)，然后按照说明完成安装。请注意，您的计算机可能会在安装过程中重新启动，您无需执行任何操作。OS X将自动继续安装到外部硬盘驱动器上，而不是启动到您的OS X内部版本。
在本文的最后，我将向您展示如何启动到外部硬盘驱动器，如果您最终使用的是App Store 方法(App Store method)，请跳过。请注意，默认情况下，Mac将直接启动到外部硬盘驱动器，直到您对其进行更改。
安装OS X(OS X)的第二种方法是重新启动Mac 并(Mac and press)按住COMMAND + R键。这将加载OS X Recovery。
OS X Utilities 屏幕(OS X Utilities screen)将出现，您要在此处单击Reinstall OS X。再次(Again)，您将浏览一些基本屏幕，但是当您进入硬盘屏幕(disk screen)时，再次单击Show All Disks。
使用这种方法，您必须使用您的Apple ID 和密码登录，(Apple ID and password)以便可以从 Apple 的服务器下载整个OS X 安装程序。(OS X installer)无论您选择哪种方法(Whichever method)，将OS X安装到外部硬盘驱动器都需要 15 到 30 多分钟。
在安装OS X时，您的计算机将重新启动几次。请注意，当它最终启动到OS X时，即是在您的外部驱动器上运行的版本。要在内部和外部驱动器之间来回切换，您必须重新启动计算机并按住OPTION键。
当你这样做时，你应该看到至少四个图标。就我而言，我有五个，因为我使用Boot Camp安装了 Windows 。无论如何(Anyway)，灰色的MacBook和Recovery 10.11.2图标适用于我的内部OS X，橙色的OS X和Recovery 10.11.3 图标( Recovery 10.11.3)适用于安装在我的外部驱动器上的版本。
使用箭头键选择要从哪个驱动器启动，然后只需按Enter即可。如果您有更新的Mac和支持USB 3.0的(USB 3.0)USB 驱动器(USB drive)，那么一切都应该运行得相当快。总的来说，这是一个相当简单的过程，我花了不到一个小时的时间就让一切正常工作。如果您有任何问题，请随时发表评论。享受！
Install, Boot, and Run Mac OS X From an External Hard Drive
Looking for a way to install and run OS X on an еxternal hard drive? Thіs can be useful for a couple of different reasons. Firstly, it allows you to run another copy of OS X without needing any additiоnal Mac computer.
Also, since you can run a full copy of OS X on the external drive, it can be used for troubleshooting purposes on other Macs or it can be as a kind of virtual OS X. I’ve already written about how you can install OS X in VMware Fusion, but that takes up space on your Mac. Using an external drive, you can save space on your Mac, though it might be a bit slower if you are using USB 2.0.
In this article, I’ll walk you through the requirements and steps to install OS X onto an external hard drive.
Format External Hard Disk
The first thing you’re going to need to do is format the external hard drive properly. The file format has to be Mac OS X Journaled and you have to use the GUID partition map. To do this, open Disk Utility and connect the drive to your Mac.
Under External in the left hand menu, click on your external hard drive and then click on the Erase button. Make sure you backup any data before you erase the drive. When you click Erase, a dialog will pop up where you can configure some options.
Give your drive a name, choose OS X Extended (Journaled) for Format and GUID Partition Map for Scheme. It should only take a minute or two for the drive to be erased and reformatted. Now your drive is ready for OS X.
Install OS X
There are two ways you can install OS X on to your external hard disk: by reinstalling OS X from the OS X Utilities repair screen or by downloading OS X from the App Store and running the installer. I’ll show you both methods in case one isn’t working for you.
The easiest way is to download OS X from the App Store. Once you open the App Store, you’ll see a link on the right for the latest version of OS X (El Capitan as of this writing).
Go ahead and click the Download button to start downloading the installer. Note that if you already have that version of OS X installed, you’ll see a popup message appear asking if you still want to continue or not. Just click Continue.
Once it has been downloaded, just double-click the installer, which will be located in the Applications folder.
Keep clicking past the license agreement, etc., until you get to the screen that asks you which disk to install OS X on. By default, it is set to MacBook.
Click on the Show All Disks button and you’ll see an icon for the different disks and partitions on the Mac. I named my external hard drive OS X and that shows up in the middle.
You can also tell it’s an external hard disk because it uses the icon with the orange hard drive. Click Continue and then follow the instructions to complete the installation. Note that your computer may restart during the install and you don’t have to do anything. OS X will automatically continue installing onto the external hard drive rather than booting up to your internal version of OS X.
At the end of this article, I’ll show you how to boot up to the external hard drive, so skip down if you ended up using the App Store method. Note that by default, the Mac will start booting up directly to the external hard drive until you change it.
The second method to install OS X is to restart the Mac and press and hold the COMMAND + R keys. This will load up OS X Recovery.
The OS X Utilities screen will appear and here you want to click on Reinstall OS X. Again, you’ll go through some basic screens, but when you get to the hard disk screen, click on Show All Disks again.
Using this method, you’ll have to login using your Apple ID and password so that the entire OS X installer can be downloaded off of Apple’s servers. Whichever method you choose, it will take anywhere from 15 to 30+ minutes to install OS X onto your external hard drive.
While OS X is installing, your computer will restart a couple of times. Note that when it finally boots into OS X, that is the version running off your external drive. To switch back and forth between the internal and external drive, you have to restart your computer and hold down the OPTION key.
When you do that, you should see at least four icons. In my case, I have five because I have Windows installed using Boot Camp. Anyway, the grey MacBook and Recovery 10.11.2 icons are for my internal OS X and the orange OS X and Recovery 10.11.3 are for the version installed on my external drive.
Use the arrow keys to select which drive to boot from and then simply press Enter. If you have a newer Mac and a USB drive that supports USB 3.0, everything should run fairly fast. Overall, it’s a fairly straight-forward process and took me less than an hour to get everything working. If you have any questions, feel free to comment. Enjoy!
