Re: Unusable system during dd to USB block device

[RVP <rvp%SDF.ORG@localhost>]

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:
/dev/rsd0
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:
https://www.freebsd.org/doc/en/books/arch-handbook/driverbasics-block.html

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.

-RVP