SOP: Tags, Size and scope Kevin Marks April 22, 2011 T10/11-206r0

NVM Express An NVM Express device uses 2 items to uniquely identify the command within the device. The combination of the two are global across all namespaces within the device (total 4 bytes). Command Identifier (CID): 2 bytes – local to the Submission Queue that the command was placed into. SQ Identifier (SQID): 2 bytes - Indicates the Submission Queue the command was placed in, in the Completion Queue Entry. SQ Identifier are included in the Completion Queue Entry, because of the ability to have multiple SQ’s map to a single CQ. SR-IOV – because an SQ_ID can be the same across VF’s, the global-ness is not across VF’s (i.e., each VF has the full namespace.)

Command Identifier Sizes for SCSI Transports ADT-2 FCP-4 iSCSI SPL-2 SRP UAS Command Identifier Size (bytes) 3 bits 2 4 8 *Scope is within the I_T Nexus

SOP SOP has several usage models where the Command Identifier can be scoped to : Entire controller Physical / Virtual Function Unique to IT_NEXUS_ID Unique to LU

Entire Controller Pros Cons Simpler for Driver Can be a memory pointer if large enough Allows creation of Compact Response IU without specifying the I_T_NEXUS_ID per Command Identifier Cons May have overlap with IOV If large may be over kill for simple end devices (e.g., SSDs)

Unique to I_T_NEXUS_ID Pros Size of Command Identifier can be made smaller Follows SAS concept of Command Identifiers per I_T Cons Requires including I_T_NEXUS_ID in compact response IU.

Unique to LU Pros Cons

Questions What should the size of Command Identifier and scope be? Currently set at 8 bytes in SOP draft and assumes global, as Compact Response only includes Command Identifier and not I_T_Nexus_ID Only SRP needs 8 bytes I_T_L_Q = 4 + 8 + 8 = 20 bytes to uniquely identify command Will the Command Identifier also be global across VF’s? Are the namespace for SCSI Commands, SOP commands and TMF’s shared? Is the mapping from a SOP transport to another transport in the bridging use case vendor specific?

Proposal(s) Reduced Command Identifier size to 32 bits; Make the 64 bit field a combination of the I_T_NEXUS_ID and Command Identifier; or Allow a reduced namespace that is specified by the target device(e.g., 32 bits and report in some identifier).

Thanks