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Re: Unusable system during dd to USB block device

On Tue, 29 Dec 2020, Thomas Mueller wrote:

What is the raw device in the case of a USB stick or USB hard drive?

On NetBSD, typically:
Raw devices have a "r" prefix.

dd to /dev/da2 (or whatever the number was) worked in FreeBSD.

On FreeBSD, there are only raw devices now:

On Linux, there are no raw devices, so you need a "direct" in {i,o}flag=
to prevent dd from clobbering the buffer/page cache.

In each case, I used bs=1m ; otherwise it uses something like 1024 or 512
bytes and is excruciatingly slow.

Yes, you would need a large block size for efficiency, otherwise for a
1GB file you would have 1GB/512 = 2M syscalls being made.

There needs to be better documentation on how to write using dd to a USB
stick from NetBSD, distinction between raw device and block device.

The examples in the NetBSD install docs only show raw devices being used,
but, perhaps a mention of the difference between raw/block devices might
be useful also.


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