Single-Path Mode:
I/O operations must be maintained for the specific channel
path over which the start I/O was initiated. Grouping exists only for device
reservation, not reconnection. Internal Disk supports only single-path mode.
Multipath Mode:
I/O operations started on one channel path may complete on
another channel path within the group. Grouping applies to device reservation,
release, and reconnection. Grouping exists only for device reservation, not
reconnection. Multipath mode is not supported.
Establish Group:
The control unit compares the IDs (11 bytes) with all other IDs
received for the same logical volume over other channel paths. A group is formed
for the addressed logical volume consisting of all channel paths with matching IDs.
Disband Group:
Each channel path in the original group for this logical volume is
placed in an Ungrouped state. If the addressed logical volume was reserved to the
channel path group at the time the command was processed, the logical volume
remains reserved only to the channel that issued the command.
Resign from Group:
The issuing channel is removed from the channel path group
for the logical volume and becomes a stand-alone channel. If the addressed logical
volume was reserved to the channel path group at the time the command was
processed, the reservation remains with the remaining members of the group.
Chaining and Restrictions:
Unit check status with sense data containing
command reject with format 0, message 2 occurs if this command:
Is not the only command in the channel program or chained directly from a
Suspend Multipath Reconnection that was the first command in the channel
program.
Is in the domain of a Locate Record or Locate Record Extended.
If any command follows this command in the chain, it is rejected with unit check
status. The sense data contains command reject with format 0, message 2.
For an invalid parameter, the command is rejected with unit check status. The
sense data contains command reject with format 0, message 4. The command is
rejected for any of the following:
The path group ID contains 11 bytes of zeros.
When a path group ID is already established for a channel path, a following
path group ID is not the same.
Table
4-32. Set Path Group ID Byte 0 Definition
Byte 0
Bits
Value
Description
0
0
1
Single-Path Mode
Multipath Mode is
Not Supported
1–2
00
01
10
11
Establish Group
Disband Group
Resign from Group
Reserved, must not be set
3–7
00000
Reserved, must be zeros
4-126
Internal Disk Subsystem Reference Guide
Summary of Contents for Multiprise 3000
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