SCSI check condition
Encyclopedia
In computer terminology, a Check Condition occurs when a SCSI
device needs to report an error.
SCSI communication takes place between an initiator
and a target. The initiator sends a command
to the target which then responds. SCSI commands are sent in a Command Descriptor Block (CDB
). At the end of the command the target returns a Status Code
byte which is usually 00h for success, 02h for a Check Condition (error), or 08h for busy.
When the target returns a Check Condition in response to a command, the initiator usually then issues a SCSI Request Sense command
in order to obtain more information. During the time between the reporting of a Check Condition and the issuing of a Request Sense command, the target is in a special state called a Contingent Allegiance Condition
.
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
device needs to report an error.
SCSI communication takes place between an initiator
SCSI initiator
In computer data storage, a SCSI initiator is the endpoint that initiates a SCSI session, that is, sends a SCSI command. The initiator usually does not provide any Logical Unit Numbers ....
and a target. The initiator sends a command
SCSI command
In SCSI computer storage, a command is the basic unit of communication. The SCSI command architecture was originally defined for parallel SCSI buses but has been carried forward with minimal change for use with Fibre Channel, iSCSI and Serial Attached SCSI....
to the target which then responds. SCSI commands are sent in a Command Descriptor Block (CDB
SCSI CDB
In SCSI computer storage, commands are sent in a Command Descriptor Block .Each CDB can be a total of 6, 10, 12, or 16 bytes, but later versions of the SCSI standard also allow for variable-length CDBs. The CDB consists of a one byte operation code followed by some command-specific parameters.A...
). At the end of the command the target returns a Status Code
SCSI Status Code
A SCSI Status Code is used to determine the success or failure of a SCSI command. At the end of any command, the target returns a Status Code byte which should be one of the following:-02h Check condition:...
byte which is usually 00h for success, 02h for a Check Condition (error), or 08h for busy.
When the target returns a Check Condition in response to a command, the initiator usually then issues a SCSI Request Sense command
SCSI Request Sense Command
The SCSI Request Sense command is used to obtain sense data from a target device.The CDB structure is:The response is a set of SCSI sense data which is structured as follows:...
in order to obtain more information. During the time between the reporting of a Check Condition and the issuing of a Request Sense command, the target is in a special state called a Contingent Allegiance Condition
SCSI contingent allegiance condition
On a computer SCSI connection, a contingent allegiance condition occurs while a SCSI device reports an error.SCSI communication takes place between an initiator and a target. The initiator sends a command to the target which then responds...
.