今天的問答環節由SuperUser提供，這是Stack Exchange的一個細分，Stack Exchange是一個社區驅動的問答網站分組。
I was reading through the manual for a Samsung portable USB hard drive that I have and came across this warning:
- Detaching the USB cable while file transfer is in progress can damage your computer and/or Portable Series External Hard Drive.
Here is the original warning:
Seriously? I am going to fry my computer by doing something that USB was explicitly designed for right from the beginning (hot-plugging)? Surely a computer does not suffer damage just because a data transfer fails.
That claim of damage is more of a legal way for a manufacturer to protect themselves on the off-hand chance that something goes wrong, meaning it is practically nonsense. It is no different than the obtuse language used in an End-User License Agreement (EULA) in the world of software; the manufacturer is right, you are wrong, our company has better lawyers than you, give us your money for a product, have a nice day, and goodbye.
I highly doubt that anything would be seriously damaged by removing a USB hard drive that is still active. So I would not live my life in fear of a warning like this.
I would however take this nonsense to mean that if something did go wrong, then the manufacturer would avoid any responsibility or liability. Instead, they would claim that the fault is yours since you failed to properly use the device as instructed in that little pamphlet most people immediately throw out when they purchase such a device.
More details below.
- Seriously? I am going to fry my computer by doing something that USB was explicitly designed for right from the beginning (hot-plugging)? Surely a computer does not suffer damage just because a data transfer fails.
Will you fry your whole computer? Most likely no. Do you increase the risk—even on a slight level—of damaging a USB port by unplugging the hard drive while it is active? I would say yes. The risk mainly comes from something like static electricity being generated between you, the computer, the USB cable and the drive port. And since the hard drive is powered and connected to some level of grounding, it becomes an attractive path for a stray static charge as explained in this blog post on the Premium USB Blog:
- ESD damage to your USB drives or ports can cause latency failures that will slow down your data transmission following static shock. Your port or device could also face more severe damage that would essentially fry it and cause it not to work at all. It could also shorten its overall lifespan. ESD can occur under simple circumstances—plugging and unplugging or flipping a nearby switch.
- Before you alarmingly back away from your computer, be comforted by the fact that the average computer user will not necessarily have to worry about it happening. However, it is still important to know about it in case you ever find yourself in a situation where ESD may occur. The odds of static shock increase once you add computer system upgrades, USB hard drives, graphics cards and other heavy duty peripherals.
- Because USB ports are hot pluggable, they need protection against static shock. With USB 2.0 data transfer rates up to 480Mbps and USB 3.0 at 5Gbps, these speeds are fast enough to spark interruptions in the signals. Many USB hubs are protected from ESD up to 2kV, but that is not always enough.
But again the risk is slight but—as that article explains—the risk does exist on some level.
Another risk is gyroscopic inertia that stems from the hard drive itself still spinning while you disconnect it. I have actually lost two external 3.5″ hard drives because I unmounted them, disconnected them, and grabbed them too quickly while the hard drives themselves were still spinning. The disorientation from me lifting one way but the gyroscopic inertia from spinning platters pulling in another direction resulted in me losing my grip on the enclosure and the hard drive crashing down onto the floor and basically making it unusable. But again, this is an edge risk.
If you ask me, overwrought details like this in the manuals are not warning you of a common risk as much as they are limiting the hard drive manufacturer’s liability if somehow your data is lost—or the hard drive dies—and you end up complaining to the manufacturer. The idea is you would conceivably call up tech support, they would ask you what you did, you might tell them you disconnected the hard drive in the middle of a transfer and then they might say, “Sorry, but we do not cover that.”
Remember, much like an End-User License Agreement (EULA), the main purpose of such documentation is not to make sure you read it as much as it is in the manufacturer’s best interest to make sure they can claim you were provided these warnings if something goes wrong from a legal standpoint.
Also, just a clarification on this point:
- I am going to fry my computer by doing something that USB was explicitly designed for right from the beginning (hot-plugging)?
The idea that USB devices can be hot-plugged into the system simply means the USB connection is hot-pluggable, but how the devices react beyond that basic connection (if hot-plugged) is entirely a different issue.
For example, I just updated my iPhone while writing this post and I had it connected to my Mac Mini via a USB cable. Sure, I could have unplugged the USB cable in the middle of the update and what would have happened? My computer would be fine and my iPhone would technically be fine from a physical standpoint, but if I unplugged it at the perfectly wrong moment, I could have bricked my iPhone.
A device being hot-pluggable simply means that the device can be connected without having to completely power down the main system to connect it or use a device probe like those SCSI probe control panels almost every Mac OS installation had back in the pre-Mac OS X days of the operating system.