[T11.3] Re: E_D_TOV and tape drives

Robert Snively rsnively at brocade.com
Tue Oct 29 15:08:04 PST 2002


INCITS T11.3 Mail Reflector
********************************
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Kevin, 

E_D_TOV is involved in link level behavior, like ACK 1 and 
next frame within a sequence. 

Protocol level responses are handled by other mechanisms.  In 
particular, ULP_TOV is a timer that is either large enough 
for the longest command or variable as a function 
of the particular command.  REC_TOV is also used if FCP-2 
recovery mechanisms are to be used.  Typical timeouts on 
a rewind may be on the order of minutes.  

I hope that helps a bit. 

Bob 


> -----Original Message----- 
> From: Kevin D Butt [ mailto:kdbutt at us.ibm.com
 ] 
> Sent: Tuesday, October 29, 2002 2:08 PM 
> To: t10 at t10.org; t11_3 at mail.t11.org 
> Subject: [T11.3] E_D_TOV and tape drives 
> 
> 
> INCITS T11.3 Mail Reflector 
> ******************************** 
> I have been looking at the following regarding E_D_TOV and have some 
> confusion regarding tape drives.  As I understand these 
> references when a 
> host issues a command (say a rewind) the target must respond within 
> E_D_TOV.  That means that a tape drive has to respond to a 
> rewind within 
> E_D_TOV (default of 2 seconds).  Obviously, a tape drive 
> cannot do this 
> using the default value of E_D_TOV.  There are other cases, 
> including data 
> transfer where 2 seconds is an unreasonable expectation.  
> Does this force 
> tape drives to modify their E_D_TOV to their longest SCSI 
> command timeout 
> value?  This would be for a long Erase which can be on the order of a 
> couple of hours. 
> 
> This would surely have some pretty odd effects on other 
> timeouts and in my 
> opinion, make for an extremely difficult multi-initiator environment. 
> 
> Do the standards really indicate that a target must give status to a 
> command within E_D_TOV?  Has this been addressed before? 
> 
> FCFS Rev 1.7a 
> 
> 21.2.1.3 E_D_TOV 
> A short timeout value is known as the Error_Detect_Timeout 
> Value (E_D_TOV). 
> The E_D_TOV is used as the 
> timeout value for detecting an error condition. The value of E_D_TOV 
> represents a timeout value for detection of a 
> response to a timed event. (i.e., during Data frame transmission it 
> represents a timeout value for a Data frame to 
> be delivered, the destination Nx_Port to transmit a 
> Link_Response, and the 
> Link_Response to be delivered to the 
> Sequence Initiator.) The E_D_TOV value selected should consider 
> configuration and Nx_Port processing param-eters. 
> The default value is 2 seconds. However, a valid E_D_TOV 
> value shall also 
> adhere to the proper 
> relationship to the R_A_TOV value. When an Nx_Port performs 
> Fabric Login, 
> the Common Service Parameters 
> provided by the Fx_Port specify the proper value for E_D_TOV. 
> When an Nx_Port performs N_Port Login in a point-to-point 
> topology, the 
> Common Service Parameters provided 
> by each Nx_Port specify a value for E_D_TOV. If the two 
> values differ, each 
> Nx_Port shall use the longer time. An 
> FC_Port may determine another FC_Port's value for E_D_TOV via the Read

> Timeout Value (RTV) ELS (see 
> 
> 
> FCP 2r07a 
> 11.6 Upper Level Protocol Time-out (ULP_TOV) 
> ULP_TOV is an operation-specific timer maintained by the Upper Level 
> Protocol. ULP_TOV is used to time the 
> completion of Exchanges associated with ULP operations. Since 
> the amount of 
> time required varies depending 
> upon the operation, the value assigned for this timer is 
> determined by the 
> operation being timed. Some 
> operations may require extended periods of time to complete. 
> ULP timers take into account response time increments caused 
> by command 
> queuing and multi-initiator 
> congestion 
> 
> 11.2 Error_Detect Time-out (E_D_TOV) 
> E_D_TOV is a general error detect time-out value. Its use is 
> specified in 
> FC-FS, FC-AL, FC-PLDA, FC-FLA, and 
> FC-TAPE. For FCP-2 Sequence recovery, it is used to time the 
> following: 
> a) the maximum time permitted for a Sequence Initiator between the 
> transmission of consecutive data 
> frames within a single Sequence; 
> b) the minimum time that a Sequence Recipient shall wait for 
> the reception 
> of the next frame within a single 
> Sequence before recognizing a Sequence time-out; and 
> c) the minimum time a Sequence Initiator shall wait for an 
> ACK response 
> before it considers the ACK to be 
> missing and begins recovery actions. 
> 
> Thanks, 
> 
> Kevin D. Butt 
> Fibre Channel & SCSI Architect 
> IBM Tape Microcode, 
> 6TYA, 9000 S. Rita Rd., Tucson, AZ  85744 
> Tie-line 321; Office: 520-799-5280, Lab: 799-2869, Fax: 
> 799-4138, Email: 
> kdbutt at us.ibm.com 
> 
> 
> 
> To Unsubscribe: 
> mailto:t11_3-request at mail.t11.org?subject=unsubscribe
<mailto:t11_3-request at mail.t11.org?subject=unsubscribe>  
> 
> 
> 


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RE: [T11.3] E_D_TOV and tape drives Kevin, E_D_TOV is involved in link level behavior, like ACK 1 and 
next frame within a sequence. Protocol level responses are handled by other mechanisms.  In 
particular, ULP_TOV is a timer that is either large enough 
for the longest command or variable as a function 
of the particular command.  REC_TOV is also used if FCP-2 
recovery mechanisms are to be used.  Typical timeouts on 
a rewind may be on the order of minutes.  I hope that helps a bit. Bob 
> -----Original Message----- 
> From: Kevin D Butt [mailto:kdbutt at us.ibm.com] 
> Sent: Tuesday, October 29, 2002 2:08 PM 
> To: t10 at t10.org; t11_3 at mail.t11.org 
> Subject: [T11.3] E_D_TOV and tape drives 
> 
> 
> INCITS T11.3 Mail Reflector 
> ******************************** 
> I have been looking at the following regarding E_D_TOV and have some 
> confusion regarding tape drives.  As I understand these 
> references when a 
> host issues a command (say a rewind) the target must respond within 
> E_D_TOV.  That means that a tape drive has to respond to a 
> rewind within 
> E_D_TOV (default of 2 seconds).  Obviously, a tape drive 
> cannot do this 
> using the default value of E_D_TOV.  There are other cases, 
> including data 
> transfer where 2 seconds is an unreasonable expectation.  
> Does this force 
> tape drives to modify their E_D_TOV to their longest SCSI 
> command timeout 
> value?  This would be for a long Erase which can be on the order of a 
> couple of hours. 
> 
> This would surely have some pretty odd effects on other 
> timeouts and in my 
> opinion, make for an extremely difficult multi-initiator environment. 
> 
> Do the standards really indicate that a target must give status to a 
> command within E_D_TOV?  Has this been addressed before? 
> 
> FCFS Rev 1.7a 
> 
> 21.2.1.3 E_D_TOV 
> A short timeout value is known as the Error_Detect_Timeout 
> Value (E_D_TOV). 
> The E_D_TOV is used as the 
> timeout value for detecting an error condition. The value of E_D_TOV 
> represents a timeout value for detection of a 
> response to a timed event. (i.e., during Data frame transmission it 
> represents a timeout value for a Data frame to 
> be delivered, the destination Nx_Port to transmit a 
> Link_Response, and the 
> Link_Response to be delivered to the 
> Sequence Initiator.) The E_D_TOV value selected should consider 
> configuration and Nx_Port processing param-eters. 
> The default value is 2 seconds. However, a valid E_D_TOV 
> value shall also 
> adhere to the proper 
> relationship to the R_A_TOV value. When an Nx_Port performs 
> Fabric Login, 
> the Common Service Parameters 
> provided by the Fx_Port specify the proper value for E_D_TOV. 
> When an Nx_Port performs N_Port Login in a point-to-point 
> topology, the 
> Common Service Parameters provided 
> by each Nx_Port specify a value for E_D_TOV. If the two 
> values differ, each 
> Nx_Port shall use the longer time. An 
> FC_Port may determine another FC_Port's value for E_D_TOV via the Read 
> Timeout Value (RTV) ELS (see 
> 
> 
> FCP 2r07a 
> 11.6 Upper Level Protocol Time-out (ULP_TOV) 
> ULP_TOV is an operation-specific timer maintained by the Upper Level 
> Protocol. ULP_TOV is used to time the 
> completion of Exchanges associated with ULP operations. Since 
> the amount of 
> time required varies depending 
> upon the operation, the value assigned for this timer is 
> determined by the 
> operation being timed. Some 
> operations may require extended periods of time to complete. 
> ULP timers take into account response time increments caused 
> by command 
> queuing and multi-initiator 
> congestion 
> 
> 11.2 Error_Detect Time-out (E_D_TOV) 
> E_D_TOV is a general error detect time-out value. Its use is 
> specified in 
> FC-FS, FC-AL, FC-PLDA, FC-FLA, and 
> FC-TAPE. For FCP-2 Sequence recovery, it is used to time the 
> following: 
> a) the maximum time permitted for a Sequence Initiator between the 
> transmission of consecutive data 
> frames within a single Sequence; 
> b) the minimum time that a Sequence Recipient shall wait for 
> the reception 
> of the next frame within a single 
> Sequence before recognizing a Sequence time-out; and 
> c) the minimum time a Sequence Initiator shall wait for an 
> ACK response 
> before it considers the ACK to be 
> missing and begins recovery actions. 
> 
> Thanks, 
> 
> Kevin D. Butt 
> Fibre Channel & SCSI Architect 
> IBM Tape Microcode, 
> 6TYA, 9000 S. Rita Rd., Tucson, AZ  85744 
> Tie-line 321; Office: 520-799-5280, Lab: 799-2869, Fax: 
> 799-4138, Email: 
> kdbutt at us.ibm.com 
> 
> 
> 
> To Unsubscribe: 
> mailto:t11_3-request at mail.t11.org?subject=unsubscribe 
> 
> 
> 
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