Subject: Re: scsi tapes
To: Olaf Seibert <>
From: Matt Ragan <>
List: current-users
Date: 02/20/1995 10:41:23
>At boot time, the kernel configuration finds out what devices there
>are, which is very nice. However, said devices need to be turned on to
>be recognised. Fair enough.
>But what if you have a scsi tape unit that's mostly turned off (because
>you don't need it very often) and so you reboot without the tape unit
>being turned on. With Linux you absolutely need to reboot before you
>can use your tape.
>Could NetBSD do better? (Not only for scsi buses necessarily but on any
>bus that could potentially have devices that are not switched on at
>boot time)
>I realise that the dynamic mapping of scsi targets to devices (st*
>at scsibus? target ? lun ? ) could not work, but a fixed mapping could.
>(Or am I being silly and it works already - I cannot try this myself).

We have the same problem with a disk device.  We have a firewall machine
running NetBSD-1.something-or-other that we have set up so that the
entire system is mirrored onto an external drive, and the internal drive
contains just what it needs for day-to-day operations, and no more.
There are symbolic links for all of the files that have been removed
from this disk to /mnt; e.g. /usr/bin/cc is a link to /mnt/usr/bin/cc.
This external drive is physically turned off except when maintenance
is needed on the system.  Then the drive is turned on, mounted, and the
system behaves like a fully loaded system, with access to all of the
tools and utilities.

When we were previously running under SunOS, we could define sd0 and sd1
in the config, and the kernel would find the drives dynamically when they
were accessed after they were powered on.  Under NetBSD, even though we
have sd0 and sd1 hard-coded in the kernel as target 0 and 1, if the
drive is not present at boot, we can't use the drive at all until we
reboot with the drive powered on.  After the system boots, we can turn
the drive off and run just fine, however.

Matt Ragan  (  Motorola/IBM Somerset PowerPC Design Center
Network Administrator          Systems/Network Engineering  (512) 795-7298
9737 Great Hills Trail         Austin, Tx  78759        FAX (512) 795-7519