Open SCSI Integrator's Manual for NonStop S-Series Servers

The Open SCSI I/O Process (IOP)
Open SCSI Integrator’s Manual for NonStop Servers—422988-002
4-15
SIM Queue Operations
SIM Queue Operations
The Open SCSI implementation of the SCSI Interface Module (SIM) queue and its
operations is derived from the existing queuing mechanism within the I/O subsystem.
The rules of operation that are specific to the Open SCSI interface are:
•
Freezing the SIM queue results in setting the I/O subsystem’s queue to a level that
prevents normal I/O operation.
•
The IOP can initiate I/O recovery operations even when the SIM queue is frozen.
•
Operations that have the SIM queue priority flag set have sufficient priority to be
dispatched even if the SIM queue is frozen.
•
A ten-second timer starts when the SIM queue experiences an application-related
freeze. If the application does not release the SIM queue before the timer times out,
then the IOP automatically releases the SIM queue.
•
The SIM queue freeze-disable flag thaws a SIM queue only if the flag is set in a
request from the same process that froze the SIM queue.
IOP Status Values
The Open SCSI IOP returns several kinds of status values that should be checked to
determine whether a requested command was successful and, if not, what caused the
error. The different kinds of status values returned are listed here in the order in which
they should be checked for locating error conditions, and described following the list:
1. File-system (FESTATUS) error-code values
2. Buffer-status values
3. CAM-status values supported by the Open SCSI passthrough mode
4. SCSI-status values returned by the peripheral device in response to the CAM
Operation Execute SCSI I/O
File-System (FESTATUS) Error-Code Values
Returned Guardian file-system (FESTATUS) error-code values indicate either normal
operation (the value FEOK), errors, or other special conditions. Many programs display
messages containing Guardian file-system error codes on the user’s terminal. These
messages typically contain a short explanation of an error followed by a corresponding
error-code number. For example:
WARNING - $VOLUME.SUBVOL.FILE CPU POWER FAILED, THEN RESTORED
ERR 230
File-system error codes are fully described in the Guardian Procedure Errors and
Messages Manual. Table 4-6 maps Guardian file-system error codes to the
corresponding Open SCSI FESTATUS literals returned by the IOP and gives the
meaning or error cause for each.