Dell PowerVault ML6000 - Manual (Page 16)

6 SCSI Command Support
For a complete list of all possible sense data and their causes, refer to Request Sense – 03h on page 70.
This status information will not be separated by individual commands.
Status values of Condition Met, Intermediate Condition Met, and Queue Full are not currently used. The
Initiator should issue a Request Sense command to determine the precise cause of the Check Condition
status and clear it.
Response data, however, will be documented as applicable for each command, and included as part of the
command section.
Unit Attentions
Unit Attentions will be queued by the library as necessary to report all events and conditions. They are
presented in the order of their occurrence (first in, first out). Unit attentions are generated for the following
conditions:
• A power on or a reset (external or internal) occurred
• A library door closed, or a transition from not ready to ready occurred
• A mailbox closed
• A firmware update completed
• A persistent reservation has been preempted or released, or a registration has been preempted
• Mode parameters have changed
Resets
Either a Power On Reset or a SCSI Reset resets the library. When reset, the library does the following:
• Returns to Bus Free
• All non-persistent reservations are cleared
Common CDB Fields
Each Command Descriptor Block contains a Logical Unit Number (LUN) field as well as a Control byte field.
The LUN field is bits 5-7 of byte 1 and is there only for legacy compatibility. Logical Unit selection should be
accomplished via the Identify message.
The Control byte is shown in the following table. It is always the last byte of a CDB, regardless of the size
of the CDB.
Vendor Specific – This field is used to provide additional data or control for a command. Specific uses (if
any) are described within the applicable commands.
Normal Auto Contingent Allegiance (NACA) – If this field is set to 0, the initiator should issue a REQUEST
SENSE command immediately following receipt of a Check Condition. If this field is set to 1, ACA support
will be provided.
Flag – This field is not supported and must be set to 0.
Link – This field is not supported and must be set to 0.
Table 5 Control Byte
Bit
Byte
7 6 5 4 3 2 1 0
last Vendor Specific Reserved NACA Flag Link