Unconditional Reserve
Description:
The Unconditional Reserve command transfers 32 bytes of sense
data to the channel. This command terminates the addressed logical volume’s
allegiance or reservation to a channel path or path group, and establishes a device
reservation to the channel path group of the channel sending the command.
This command operates even if the logical volume is busy or not ready. See
“Effect of Subsystem and Device State on Status Presented to Command” on
page 2-5 for the operation of this command when other subsystem and device
status conditions occur.
This command includes all the Sense command functions. Also, it reserves the
logical volume to the channel path group or the channel path sending the
command. If the command is received on a logical volume that is grouped, it is
reserved to the path group. If the command is received over a channel path where
the logical volume is not grouped, the logical volume is reserved to that channel
path. The logical volume reservation lasts until the LPAR successfully completes a
Device Release command to the logical volume or until all reserved paths are reset
by a system or power-on reset.
Warning:
The system operator must establish control of the logical volume before
the Unconditional Reserve command can be issued. Issuing this command can
interrupt operations on other LPARs. Device control is established if the LPAR has
the logical volume reserved, or the LPAR has a CCW chain in progress (between
the Start I/O instruction with a condition code 0, and the ending interruption). If the
LPAR sends this command to a logical volume not assigned to it, one of the
following conditions may occur in the other LPAR. If the logical volume is:
Reserved, the reservation is reset and the logical volume becomes reserved to
the channel sending the Unconditional Reserve command.
Disconnected between chained commands, an interruption will be lost.
Active when the command is processing, the control unit presents a
recoverable equipment check.
Idle and not reserved, there is no effect.
Chaining and Restrictions:
Unit check status with the sense data containing
command reject with format 0, message 2 occurs if:
This command is received in the domain of a Locate Record or Locate Record
Extended command.
This command is not the first command in the channel program or chained
directly from a Suspend Multipath Reconnection command that was the first
command in the chain.
Unit check with the sense data containing equipment check with format 3, message
F will be sent to a channel if:
Any I/O chain was interrupted by this command.
Hex Code
Data Address
Count
14
The main storage location for the first sense byte.
32
Chapter 4. Command Descriptions
4-121
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