I've long been looking for a way to write protect one USB drive, while backing it up to another USB drive. And also to be able to mount USB drives as read-only to be confident of their contents remaining safe.

I've in the past wondered about using a forensic write blocker but they are expensive and I've always wondered if they're overkill. All I really want is the USB inline equivalent of a write protection switch. I just noticed there are cheap USB inline adapters like this one that purport to write block. Would it be OK to use one of these to write protect a drive I'm trying to back up?


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    You didn't specify an OS (please edit the question and add a tag). For example, if you manually mount USB drives on Linux, it's easy to mount them read-only (just add -o ro to the mount command). The protection happens on the OS level, so you need to trust the OS. – dirkt Jul 2 at 13:43
  • dirkt - I added the OS (Windows 10). I would totally be trusting the OS if I were using Linux for this. I'm not aware of any Windows equivalent of doing a Linux read-only mount, but that's exactly the equivalent I'm looking for. While I'm not a Windows despiser (I use both Windows and Linux) there are some really unfortunate omissions in Windows and this is one of them. – pz99 Jul 2 at 18:28
  • There used to be a working method in Win7, using the registry. You could turn on the read-only flag in the registry, and plug in a drive, and that drive would be read-only. Then turn off the same flag, and plug in another drive, and that new drive would be writable while the first one remained read-only. This no longer seems to work in Win10-- in my experience the flag either goes into immediate effect for all drives (including ones that were plugged in earlier), or doesn't go into effect at all-- it seems quirky. – pz99 Jul 2 at 18:32
  • Win10 does have the Group Policy Editor method which has sometimes worked for me but lately it seems to go into immediate effect for all drives, so you can't have one drive read only and another write only. – pz99 Jul 2 at 18:32
  • @dirkt - note that -o ro doesn't actually guarantee that no writes will occur... ref, ref – Attie Jul 2 at 18:38

I just noticed there are cheap USB inline adapters like this one that purport to write block.

These little devices don't purport to block writes, they block all data / communications and allow only power through.

Some of the smaller / cheaper / older options will simply disconnect the data signals from one side to the other, the more expensive options will negotiate for more power to facilitate faster charging, but still maintain logical isolation between the host and device.

These are often used to charge devices with untrusted USB power sources - for example in airports.

Blocking only write operations, but permitting enough communications to present a usable (albeit read only) device is not a simple task, which is why forensic disk controllers will often be physically relatively large, require power, and be expensive.

These tools are also typically used only to make images of whole storage devices, rather than access the device's filesystem(s) in an interactive way.

Why do you feel the need to use a write blocker during backups?

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  • That's useful information. It sounds like these little devices are NOT the way to go for what I'm looking to do. Which is unfortunate b/c as far as I can tell Windows has no ability to make a drive temporarily read-only in the manner I'm looking for (as if it were a switch like there is on an SD card or some enclosures.) As for why to use a write blocker, that's to protect against my either doing something stupid or a ransomware attack while backing up an important drive. – pz99 Jul 2 at 18:30
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    I'm not totally convinved by your reasoning for wanting read only access... but it also feels churlish to suggest that you shuld "just be careful"... – Attie Jul 2 at 18:39
  • I've heard this answer many times, and yet I've blown it enough times (not many, but twice is enough) to feel the need to do this. And I loved my Win7 registry solution and used it all the time. I really don't think it's a crazy thing to want, although I understand that sometimes people think it is. Linux actually has this feature and nobody is begging them to remove it, after all! – pz99 Jul 2 at 19:55

Your drive blocker either works or not. The question makes as much sense as "Is it OK to use a condom?". What response do you expect? This question is opinion-based and should be deleted.

From reading the article description you should distinguish between "data blocker" and "write blocker". This is just a "data blocker" which is nothing more and less than a power supply adapter.

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  • Question may not be interesting to you, but it isn't opinion based. – pz99 Jul 2 at 18:34
  • I wasn't asking "is it OK to use them" in a philosophical sense, but whether they would function to do what I was looking to do, which is backup. I can't put the entire question in the title. – pz99 Jul 2 at 18:36

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