Dell PowerVault ML6000 - Manual (Page 17)

PowerVault ML6000 SCSI Reference Guide 7
Reserved Fields
Reserved fields are not checked, and no error will be sent if they contain non-zero values.
Online/Offline Operation
Each Media Changer device can be placed in either an online or offline mode. The purpose of these modes
is to configure whether the Media Changer is being controlled by a SCSI initiator or by the operator panel.
When the Media Changer is online, a SCSI initiator is controlling it and all SCSI commands are supported.
When the Media Changer is offline, the operator panel is controlling it, and the only allowed SCSI
commands are INQUIRY, REPORT LUNS, and REQUEST SENSE. All other commands will respond with
a check condition, along with an ASC/ASCQ of 04/8D (unit offline).
The controller device is not affected by the online/offline mode of the Media Changer.
Supported Interfaces
SCSI Parallel and Fibre Channel interface types are supported as described below.
SCSI Parallel Interface Support
The library supports parity checking on the SCSI Parallel interface. It will attempt to retry when parity errors
are detected, but if unsuccessful will attempt to respond with a Check Condition indicating in which phase
the parity error was detected.
If permitted by the initiator, the library will also support SCSI disconnect for commands that take a lengthy
time to process, such as MOVE MEDIUM. Disconnect privilege is granted by the initiator via the Identify
message.
Supported Messages
The SCSI message system (Message In/Message Out) allows communication between an initiator and a
target for the purpose of physical path management. The supported messages are shown in the following
table. The direction is relative to the initiator.
Table 6 Supported SCSI Messages
Message Code Direction Description
COMMAND COMPLETE 00h In This message is sent from the target to an initiator
to indicate that the execution of a command
completed and valid status has been sent to the
initiator.
EXTENDED MESSAGE 01h Out This message is sent from an initiator to the target
to attempt to negotiate synchronous or wide data
transfers. The library supports both.
SAVE DATA POINTERS 02h In This message is issued before every disconnect
message following a Data In or Data Out phase.
The message is not sent when disconnecting after
a Command Descriptor Block (CDB) that did not
transfer data.