[T11.3] E_D_TOV and tape drives

Kevin D Butt kdbutt at us.ibm.com
Tue Oct 29 14:08:07 PST 2002


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



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