Re: Accessing a RAID disk attached externally via USB

[Malcolm Herbert <mjch%mjch.net@localhost>]

On Tue, Jul 09, 2019 at 08:39:11PM -0400, Greg Troxel wrote:
|mlelstv%serpens.de@localhost (Michael van Elst) writes:
|> frank%phoenix.owl.de@localhost (Frank Wille) writes:
|>>It appears as sd0 with a RAID partition in sd0a. How can I access an
|>>FFS partition inside the RAID without changing anything on that RAID
|>>disk?
|
|I am assuming that this is raidframe and the original system is NetBSD.
|
|If you have raid autoconfig enabled, I'd expect the raid set to just
|appear, similar to how I would expect the original setup worked.

a note of caution on this however - I have had experience with
a external device and both my internal drive(s) using raidframe
autoconfigure ... during boot one or other will be remapped to different
raidN ID ... I'd gotten lucky in that my internal disks ended up on
raid0 where they were meant to be and the external was remapped to raid7
(iirc)

unfortunately, this change stays with the raidframe device, so when
you insert that external disk back into it's original host the kernel
on there can't boot because the root fs pivot fails ... some judicious
booting from an install CD got me out of that, but it was a definite
head-scratching moment to start with ...

|> You could create a RAID set that includes that disk and access the
|> raidframe device.
|>
|> You could also calculate the offset and size of the partition inside
|> the RAID volume and manually add a wedge with these parameters.
|
|The raid header is 64 blocks, so a wedge that is like sd0a but starts
|64 sectors later and ends in the same place should function like
|raid0d. Then of course you may have a disklabel or gpt inside the raid.

this seems the safest way ... of course if you want to absolutely
make sure you don't modify your original disk, use a hardware
duplicator first and use the copy (but be very very certain you haven't
accidentally put them in the wrong way around ... btdt)

Hope that helps,
Malcolm

-- 
Malcolm Herbert
mjch%mjch.net@localhost