SCSI Primary Commands - 2.pdf

18 July 2001 T10/1236-D Revision 20Most log pages contain one or more special data structures called log parameters (see table 124). Log parametersmay be data counters of a particular event(s), the conditions under which certain operations were performed, or listparameters that contain a character string description of a particular event.Table 124 — Log parameterBitByte7 6 5 4 3 2 1 00 (MSB)PARAMETER CODE1 (LSB)2 DU DS TSD ETC TMC LBIN LP3 PARAMETER LENGTH (n-3)4PARAMETER VALUEnEach log parameter begins with a four-byte parameter header followed by one or more bytes of PARAMETER VALUEdata.The PARAMETER CODE field identifies the log parameter being transferred for that log page.The DU, DS, TSD, ETC, TMC, LBIN, and LP fields are collectively referred to as the PARAMETER CONTROL byte. Thesefields are described below in this subclause.For cumulative log parameter values, indicated by the PC field of the LOG SELECT and LOG SENSE commands,the disable update (DU) bit is defined as follows:a) A zero value indicates that the device server shall update the log parameter value to reflect all events thatshould be noted by that parameter; orb) A one value indicates that the device server shall not update the log parameter value except in response toa LOG SELECT command that specifies a new value for the parameter.NOTE 40 When updating cumulative log parameter values, a device server may use volatile memory to hold thesevalues until a LOG SELECT or LOG SENSE command is received with an SP bit of one or a target-defined eventoccurs. As a result the updated cumulative log parameter values may be lost if a power cycle occurs.The DU bit is not defined for threshold values, indicated by the PC field of the LOG SENSE command, nor for listparameters as indicated by the LP bit. The device server shall ignore the value of the DU bit in any log parametersreceived with a LOG SELECT command.A disable save (DS) bit of zero indicates that the target supports saving for that log parameter. The device servershall save the current cumulative or the current threshold parameter value, depending on the value in the PC field ofthe CDB, in response to a LOG SELECT or LOG SENSE command with an SP bit of one. A DS bit of one indicatesthat the target does not support saving that log parameter in response to a LOG SELECT or LOG SENSEcommand with an SP bit of one.A target save disable (TSD) bit of zero indicates that the target provides a target-defined method for saving logparameters. This implicit saving operation shall be done frequently enough to insure that the cumulative parametervalues retain statistical significance (i.e., across power cycles). A TSD bit of one indicates that either the targetdoes not provide a target-defined method for saving log parameters or the target-defined method has beendisabled individually by an application client setting the TSD bit to one. An application client may disable thedpANS SCSI Primary Commands - 2 (SPC-2) 173