pdp11v/usr/man/local/man1/psel.1m

.TH PSEL 1M "3B20S only"
.SH NAME
psel, rels \- send priority select/release to a disk
.SH SYNOPSIS
.B /etc/psel
unit
.PP
.B /etc/rels
unit
.SH DESCRIPTION
.I Psel\^
sends a priority select to a disk and
.I rels\^
sends a priority release to a disk.
.I Unit\^
specifies the unit number of the disk drive to be used.
.SH WARNINGS
Note that these commands work only with \s-1DFC\s+1 Generic 2 (or later) Firmware
and only with dual-ported disks.
The
.I psel\^
command is dangerous.
These commands are intended to allow temporary remote recovery
of a dual-ported disk when an unusual form of crash
has left the disk reserved by the dead system.
The priority select immediately overrides the reserve of the other system.
Using this command when the other system is actively using the disk
will cut that system off in the middle of use.
If a write is in progress, an error could even be induced on the disk.
Use
.I psel\^
only after making sure the other system has crashed and that
attempts to bring the disk in service time out.
Once
.I psel\^
is used on a disk,
that system must issue a
.I rels\^
to that disk to make the disk accessible to the other system.
A priority select from one system does
not override a previous priority select by the other system.
If a system crashes leaving the disk priority selected,
switches in the drive must be thrown to disable the port
to allow access by the other system.
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