March 30, 1989 TO: ANSI X3T9.3 Committee Members FROM: Roger Cummings SUBJECT: ALTERNATE DEFERRED ERROR HANDLING (REVISED) | After the Tape Working Group meeting I distributed the minutes | and the proposed changes to the standards to all of the meeting | attenders. I also forwarded a copy of these documents for | inclusion in the next X3T9.3 mailing. | | However after reviewing the distributed package several of the | meeting attenders pointed out that I had omitted from the minutes | and the changes an agreement to define an additional bit in the | Attributes Parameter 6E (Slave Reconfiguration). | | An objection was also raised to some of the wording in the | proposed standard change regarding the handling of deferred | errors. | | A comment was also made that in some tape applications the method | of handling deferred errors may be changed on a reel by reel | basis, and thus it was suggested that bits be included in the | Operating Mode command to allow the Master to define the method | to be used. | | The standard to be changed was also incorrectly identified in the | first version of the memo. | | Therefore I have amended this memo accordingly, as below, with | the changes marked by a revision bar in the left margin: | | | | The Level 3 Tape Working Group that met on February 1, 1989 recommended that the following ENHANCEMENT be made to the document entitled Intelligent Peripheral Interface - Device Generic Command Set for Magnetic Tape (ANSI X3.147-1987): | 1) That section 4.6 be replaced with the following text: 4.6 Data Buffer Operation A tape slave/facility may contain buffer space capable of containing multiple blocks of data. This data buffer may contain data "read ahead" from the medium or data waiting to be written to the medium. When performing a write, a slave/facility capable of storing multiple blocks in the data buffer may: a) Transfer an operation response indicating Successful status to the master once all the write data has been transferred from the master and successfully stored in the data buffer. If an unrecoverable write error is subsequently encountered while attempting to record the data on the medium, the addressee shall generate an Asynchronous Response packet to inform the master of the failure. The master may then use the REPORT POSITION command to determine the number and addresses of the data blocks remaining to be fixed to tape. Unwritten data may then be recovered by using the READ FROM BUFFER command. or, alternatively: b) Transfer an operation response indicating Successful status to the master only when all of the write data has been successfully written to the media. If an unrecoverable error occurs anywhere in this process, then the operation response (command completion) indicates the error to the master as usual. The Master may then be able to determine the media position from the CRN in the response packet, or it may have to issue a REPORT POSITION | command. The master may then cause the addressee to clear the buffer contents, and may reissue the data that was not written on the media to the same or different media. This alternative may be useful in journalling applications in which the performance degradation of true synchronous mode due to multiple repositions is unacceptable. Note however that implementations that use this alternative must carefully consider the impact of the depth of their command queues on the usable size of their data buffer. Note also that this alternative combined with the supression of Operation Responses on Successful is almost equivalent to alternative a) above. | If method b) above is supported then ATTRIBUTES (Parameter 6E | Octet 1 Bit 0) shall be used to indicate that fact to the Master. | If both of the above methods are supported, then the Master shall | use either ATTRIBUTES or OPERATING MODE to select the method to | be used. | Addressees that "read ahead" into a data buffer shall not report an unrecoverable read error to the master until the unrecoverable data is requested by the master. Tape slaves/facilities that provide the asynchronous buffer mode shall also support a synchronous mode of operation that may be controlled by the master (i.e. the addressee shall be capable of disabling the data buffer). Enabling and disabling the data buffer is accomplished using the ATTRIBUTES and OPERATING MODE commands. In addition, a master may instruct an addressee, operating in the asynchronous mode, to synchronize its buffer and media position by issuing a POSITION CONTROL command with the Synchronize bit asserted. | The Level 3 Tape Working Group that met on February 1, 1989 also | recommended that the following ENHANCEMENT be made to the | document entitled Intelligent Peripheral Interface - Device | Generic Command Set for Magnetic Disk (ANSI X3.132-1987): | | | 1) That in Table 42 Octet 1 Bit 0 be changed from | "reserved" to "Command Complete Response on Buffer | Receipt". | | | 2) That the following new paragraph shall be added to | Section 6.3.4.14: | | (17) Command Complete Response on Buffer Receipt Bit. When this | bit is set the slave shall generate a Command Completion Response | for a Write-type Transfer command when all of the data for that | command has been received in the slave's buffer. | | | 3) That in Table 47 Octet 1 Bit 3 of Parameter 50 be | changed from "reserved" to "Command Complete Response on | Buffer Receipt". Please review the proposed enhancements, and be prepared to consider its adoption at the April plenary in St. Petersburg, FL. If there are any problems or omissions I can be reached as follows: Phone: Business (416) 826-8640 x3332 Home (416) 625-4074 (ans machine) Telex/MCI Mail: 650-289-5060 (USA) Fax: (416) 821-6363 Regards ______________________ Roger Cummings Principal Engineer, I/O and Peripherals Systems and Strategies Group Control Data Canada Ltd. 1855 Minnesota Court Mississauga, Ontario L5N 1K7 Canada #yj/rc