Boot device question

[Greg Larkin]

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Chris Pratt wrote:
> I have a server with 6 hot-swap SATA slots. It was delivered
> with the first slot empty and 5 drives set up as /dev/ad4 through
> /dev/ad12. I'd never paid attention to this until I wanted to add
> a 6th, now 4 years later. When I popped it in, I realized the
> empty bay was not 6 but rather bay 1, and of course it wouldn't
> boot. Presumably /dev/ad2 had now come alive for the first time.
> I popped out the disk, rebooted and after it was up, I plugged it
> back in (hot) and ran sysinstall. It didn't see the disk so I couldn't
> fdisk it. No device files existed for it.
> 
> I was thinking a right approach would be to change fstab to
> reference ad2 for all the system disk file systems, shutdown,
> move that drive to the first bay and plug the new drive into the
> 2nd bay. This seemed like more of a permanent solution.
> If those /dev/ad* files are created at boot dynamically,
> this should work. I've found docs that imply that they are
> dynamically discovered and created from FreeBSD 5 forward
> (auto-discovery?). Are they or do I need to create them prior to
> start up.
> 
> The thing is, there is no easy recovery from failure here since I
> have no console monitor to let me see what's going on or to fix
> fstab if it fails (counter-intuitively, the only place I can access
> the console is from remote locations ;-)), so I just want to know
> if I'm thinking straight? The plan is:
> 
> 1. Change /etc/fstab entries for ad4 filesystems to ad2
> 2. Shutdown
> 3. Put the system disk in Bay 1
> 4. Power up
> 
> Should it boot?

Hi Chris,

I don't know the answer to that question, but I do know that you can
wire physical devices to specific devices files in /dev.  I use the
/boot/device.hints file to do that.  Check this page for more
information:
http://threads.seas.gwu.edu/cgi-bin/man2web?program=scbus&section=4

Halfway down the page, you'll see directives like:

hint.da.0.at="scbus0"
hint.da.0.target="0"
hint.da.0.unit="0"

I believe you can do something similar with your ad devices, and force
the new drive to a different /dev/ad? device file that doesn't cause a
boot problem.

Hope that helps,
Greg

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