How does CAM determine the order to number drives ?

[Michael Grant]

Yes, I know this situation all to well.  In my case, I ended up
physically plugging and unplugging drives until they ended up in the
right place.  

I would sure love to see a way to fix a drive to an identifier.  This
has to be the one thing that has wasted more of my time than anything
else in freebsd.  For example, when I had a drive die on me a couple
months back, when the machine rebooted, the dead drive still in the
system, da2 became da1 and things just did not work well.

If someone knows of a way to tie physical drives to the nodes in /dev,
please let me know.  I've heard that this auto drive numbering
is a bios "feature" which is impossible to get around.

Michael Grant

On Sat, Jul 31, 2004 at 08:25:58PM +0100, Pete French wrote:
> Hi, I have a small server which boots from an
> Adaptec 2940 controller under CAM, and serves drives
> off a Compaq 4200 RAID controller.
> 
> I have spent the afternoon ttrying to upgrade the
> RAID controller from a 4200 to a 5300. The 5300 uses
> the CISS driver rather than the IDA driver, and this
> lives under CAM too. Thus my RAID drives have changed
> from being idad devices to being da devices.
> 
> Unfortunately the RAID controller gets scanned first
> so I now have a da0 and a da1 where I didnt before, and my
> root drive has moved to da2.
> 
> I can't persuade it to boot like this - it refuses to mount
> the root from da2. The simplest solution, of course, would
> be to somehow force the CAM system to scan the Adaptec
> controller first, so that the root device is back in da0
> where it belongs. But I cant find out if there is a way
> of dojing this, or indeed how the system determines the order
> at all.
> 
> Any suggestions ?
> 
> -pcf.
> 
> PS: System is 4.10-RELEASE, though I suspect this is irrelevent
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