kern/59024: dump fails on raid0b

[campbell+netbsd%mumble.net@localhost]

>Number:         59024
>Category:       kern
>Synopsis:       dump fails on raid0b
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Jan 22 09:50:00 +0000 2025
>Originator:     Taylor R Campbell
>Release:        current, 10, 9, ...
>Organization:
The NetBSDump Failedation
>Environment:
>Description:
BERTRAND Joel reports:

> [ 417509.006761] dumping to dev 18,1 (offset=253015, size=4162677):
> [ 417509.006761] dump device bad

This is raid0b and apparently it's a regression from netbsd-9 that it doesn't dump.  But why not?
>How-To-Repeat:
dump to raid0b on BERTRAND Joel's machine
>Fix:
Yes, please!