Re: devfs persistence

From: Rodger Wilson {I/O Software} (
Date: Thu Apr 27 2000 - 16:22:25 EST

It seems to me that there are two types of persistence:

a) real time reconfiguration (via lips, etc)

Right now I only fibre channel has this problem. That is the problem of
device changing their target (APLA) change while still running. These,
devices should be refered to by their WWN while in the frame work, and
then having the HBA change the WWN into an ALPA just before send the
CDB. This can be done with a simple lookup table within a HBA.

This problem may also occure if we ever see USB/FireWire drives.

b) rebooting persistence.

Here we want a computer to talk to the same device after having been
rebooted. For devices like IDE & SCSI the issue is fairly easy, we simply
want a path to represent name like disk0. But in FC we need a name to
be associated with a framework path and a paticular disk drive. This can
be handled with in the /etc/devfsd.conf


/dev/discs/disc0 /dev/ide/hd/c0b0t0u0
/dev/discs/disc1 /dev/scsi/host1/bus2/t3,4
/dev/discs/disc2 /dev/fc/host1/bus3/wwn2100002037265f98,0

Then when the system loads it creates these links & nodes even if the
drive is missing, then if io goes down to the HBA for a target the HBA can
look up the WWN and send io to the target if it is found else return
error. This would allow for persistence even if the drive was not
available untill 5 mins after reboot.

Rodger Wilson
Target and SCSI Drivers (Sun Microsystems, Inc.)
DIRECT: (303) 272-8252 HOME: (303) 499-9498
FAX: (303) 272-7793 CELL: (303) 669-7955
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