Re(2): Re(2): [SunRescue] a bit OT but...

[James Lockwood]

On Thu, 16 Mar 2000, Dave McGuire wrote:

> On March 16, Bill Bradford wrote:
> > On Thu, Mar 16, 2000 at 09:44:23AM -0500, Tim Hauber wrote:
> > > yeah?  plug them in and go, I know it isn't recommended, but I don't have
> > > problems with live SCSI changes.
> > > Tim
> > 
> > Do you parachute and bungee jump too?  Live SCSI bus changes are a
> > Bad Thing (tm).
> 
>   No way, Bill.  SCSI deals just fine with hot swaps...as it was
> designed to do.  I've done it on hundreds of machines, most of them
> Suns, starting with a Sun2/120.  It works just fine...it really
> does!

SCSI deals just fine with hot swaps if the _hardware_ can handle it.
Plugging in drives in hot swap enclosures is good.  Yanking a SCSI cable
or terminator off of a live SCSI chain and adding another device can be
dicey.  Whatever you do, it can be very difficult to make 100% sure that
the SCSI bus is quiesced.

Some of the nicer enclosures that autoterminate make this a little easier.
Plug in another case after it and the bus doesn't skip a beat.

I've done live swaps when I've had to, but unless the hardware can safely
do hot swap I try to avoid it.  To tell Solaris to reprobe the SCSI bus
after boot, force the sd driver to reconfigure and regenerate the /dev
links:

drvconfig -i sd; /usr/sbin/disks; /usr/ucb/ucblinks

This works well when you add devices, but removing a device and adding
another at the same SCSI ID is not safe.

-James