我們都知道從我們的計算機上分離USB大容量儲存裝置有正確的方法和錯誤的方法，但是相同的原理適用於MTP裝置嗎？今天的超級使用者問答帖子回答了一位好奇的讀者的問題。

今天的問答環節是由SuperUser提供的，SuperUser是Stack Exchange的一個分支，是一個由社群驅動的問答網站分組。

問題

超級使用者閱讀器RockPaperLizard想知道你是否可以簡單地拔下連線到Windows的MTP裝置上的USB插頭：

I know that after attaching a typical USB mass storage device to Windows, it is important to properly unmount the device before unplugging it in order to avoid the possibility of losing data. But for MTP devices (such as many Android devices) connected to a Windows computer via USB, is it necessary to perform any special or particular procedure before disconnecting the USB cable?

I am interested in understanding this for all versi*** of Windows (XP and later), so please include the applicable Windows version(s) in your answer.

你能簡單地拔下連線到Windows的MTP裝置上的USB插頭嗎？

答案

超級使用者貢獻者Carrein為我們提供了答案：

When plugging in USB mass storage devices, it gives a host computer undifferentiated access to the mass storage. It assumes absolute control over the file system similar to that of a hard drive.

As such, unless explicitly commanded by the host system to sever the connection between the devices, there is a chance that the host computer might corrupt the file system. Hence, the “Safely Remove Hardware and Eject Media” message.

However, MTP, or Media Transfer Protocol, operates at the file level rather than as a large unit of mass storage at the block level. When plugging in a device such as an MTP device, the host system queries the files on the device.

This is often maintained as a database or index in the root file system of the MTP device. The MTP device’s system does not have to rescan the entire device when its content is modified; it only needs to update the database/index.

The host system can then send a message to the device requesting that a file be downloaded, which will be sent by the device after acknowledging the signal. Deleting files works much the same way. The host system sends a message to the device, marking a file for deletion, then the device removes the file upon acknowledging the signal.

This works much like a transactional file system, where either the file is modified or it is not. The storage will not be affected by a failed transfer. This is also the reason why MTP only allows one file transfer at a time (atomic file transfer), so that corruption cannot occur as operati*** are run sequentially.

So yes, you can just pull the USB plug on your device.

Further Reading: Media Transfer Protocol [Wikipedia]

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