FC-Tape December 98 Minutes
stewart at hpbs3928.boi.hp.com
Fri Dec 18 13:40:32 PST 1998
* From the T10 Reflector (t10 at symbios.com), posted by:
* Stewart Wyatt <stewart at hpbs3928.boi.hp.com>
Fibre Channel Tape Profile Meeting T11/98-619v0
Tucson, Arizona, 16 December 1998
Stewart Wyatt, Secretary
1. Introductions: Chairman Dale Lafollette (STK) called the meeting
called to order at 12:35 PM and had the participants introduce
2. Approval of this Agenda: T11/98-592v0
The agenda was approved with the addition of a new item, 6.1 FCP-2:
3. Approval of 11/3 Minutes: T11/98-567v0
Minutes were approved.
4. Review of Old Action Items:
Secretary Stewart Wyatt, HP, reviewed the action items.
#1 Stewart Wyatt will get a resolution on HP SCSI command comments.
Resolved in HP letter ballot comments.
#2 Erich Oetting will propose to the T10 working group that the Write
Exclusive Persistent Reservations be made illegal for SSC devices.
Erich was not present, deferred to next T10 meeting.
#3 Erich Oetting will propose to the T10 working group that the
communications devices command set be made obsolete. Erich was not
present, deferred to next T10 meeting.
#4 Dave Peterson will attempt to document EOD behavior more precisely
in SSC. Dave has posted a new version of the SSC, deferred to the next
#5 Dave Peterson will enter a letter ballot to correct the I5 IU
specified in FC_Tape. Completed.
#6 Bob Snively will take a recommendation to the T10 working group to
obsolete the Flag bit in the Control byte. Completed.
#7 Bob Snively will enter a letter ballot comment to make FC-Tape
compatible with the changes in FCP-2 regarding handling of CRN's.
(18.104.22.168 and Annex D.) Completed.
#8 Bob Snively will enter a letter ballot comment to remove annexes
form FC-Tape for items documented in FCP-2. Completed.
5. Letter Ballot Comment Review:
Editor Dave Peterson, STK, had brought a list of letter ballot
comments that he wanted to have the group review. The other comments
he felt he could handle on his own.
#1. Bob Snively (SUN) Comment ID 47. The REC does not provide enough
information to create a properly formed SRR.
Bob Snively, SUN, referred to figure 10 in Annex B.The REC accept does
not provide relative offset for resumption of a transfer with the
Enable Modify Data Pointers (EMDP) bit set. Matt Wakeley, HP,
responded that this figure was just requesting the retransmission of
the transfer ready and would not exhibit a problem.
Neil Wanamaker, Crossroads, suggested that Figure 17 in Annex B was a
better example as it includes an error on a data transfer. The REC
indicates the number of bytes transferred but with the EMDP bit set
the sequences are not required to be sent in-order so it is not always
clear where the recovery should begin. Bill Martin, Gadzooks, proposed
that on a read failure the SRR could request the RO at the beginning
of the transfer. As the problem occurs when reads operations are
streamed, Matt Wakeley suggested precluding streaming reads, which Bob
observed would seriously limits tape performance. Dale suggests
retransmitting the whole record again, which he clarified was the
entire command, typically 256K bytes. Write transfers do not have the
problem since the transfer ready limits the recovery to only the last
Two possible solutions were considered: Specify the REC and SRR more
completely or give the host the option that redo the entire transfer.
Neil Wanamaker noted that reads are less common than writes so
reducing the performance of the read may be acceptable. Dal Allan,
ENDL, noted that recovery is a high anxiety moment - reducing the
performance of the recovery may not be good.
Rob Basham, IBM, interjected a case he was concerned about which he
called the fixed block problem. In this case recovery becomes more
difficult when it starts in the middle of a physical block. Dale
replied that the solution is to not release the data buffer until you
are certain that the host got it all so that you do not have to
recover the data from the tape.
The conclusion was to recover streamed reads from a relative offset of
zero if there is any ambiguity, meaning that the entire command is
re-transferred. It there is no ambiguity, recovery can begin from some
later position in the transfer.
Bob Snively, who is the editor of the FCP-2, noted that some of these
issues belong in the FCP-2. He would like the issues to be resolved by
this group and placed in annexes in the FC-Tape document. He will put
them in the FCP-2 and they can be removed from tape document before it
Agenda item 6.1
For the convenience of the editor, there was a break in the letter
ballot review while Bob Snively reviewed the FCP-2 status.
Bob provided an overview of the changes in FCP-2 from FCP. The first
topic was mode pages. The first one Bob mentioned was the
Disconnect-reconnect page. The next was the Fibre Channel Logical Unit
Control page (18). Interesting bits on this page are the Maximum Burst
Size field (which defines the maximum sequence length) and EMDP bit.
The next mode page is the Fibre Channel Logical Unit Control page
which contains the EPDC which enables the precise delivery function
(command CRNs). The last one mentioned was the Fibre Channel Port
Control Page (19) which contains port configuration bits.
In reviewing this page, Tak Seto, Quantum, noted that these
definitions were inconsistent with previous documentation. Bob noted
that these functions had been defined in several different documents
and that the FCP-2 would be the final authority.
Pak noted that DTOLI requires that FC-AL-2 behavior be required and
would obsoletes FC-AL devices. He asked if FCP-2 should require FC-AL2
compliance. This was discussed. It was noted that many of the bits
required FC-AL2 to be implemented anyway. This secretary was of the
opinion that the discussion conclusion was that AL2 compliance was
required. Jeff Williams, Western Digital, and Jim Coomes, Seagate,
agreed that these features needed to be reviewed and discussed. Having
Bob collect them into the FCP-2 is providing a forum for the review to
Jim Coomes noted that an additional bit had been proposed for the Port
Control page. He called it Enable auto response and it had been
located in byte 4, bit 0. This bit is necessary because some
initiators cannot accept the response in the same latency as the data
on a read operation.
George Penoki, IBM, expressed concern that Bob Snively, The FCP-2
editor was making technical changes to the FCP-2 without obtaining
approval by submitting a formal request to the appropriate groups. Bob
replied that the some of the tape development will be moved into FCP-2
without a new proposal, as he felt this requirement was met by the
tape discussions. He considered this presentation to be the formal
proposal for several of the features discussed.
Other changes to the FCP-2 include adding Confirmed delivery, RR_TOV,
an extended CDB proposal, eliminating operation associators,
eliminating sequences with mixed command and data as well as mixed
data and response. The concept of confirmation is being dropped.
After Bob concluded the agenda was returned to agenda item 5,
reviewing the letter ballots comments:
#2 Matt Wakeley (HP) Comment titled: Public behavior not documented.
Stewart Wyatt noted that there are several places in the profile that
presume private behavior that need to be corrected. The biggest area
of concern with public behavior was the subject of authentication
after a loop initialization. Currently the profile refers to the FLA
for public initialization and copies material from the PLDA for
private loop initialization. Jeff Stai, Brocade, said he had heard
some hallway talk about a suggestion to generate a generic SCSI and
Fabric behavior. Bob Snively thought that would belong in FCP-2.
Stewart Wyatt felt that a common initialization process needed to be
defined that demonstrated the process of discovering that the fabric
was not present and proceeding to private loop initialization. Stewart
was also interested in how hosts on remote loops were informed of
initialization changes. Jeff said that was done through state change
notification. Stewart noted that this was prohibited in this profile
which he thought was an indication that the process had not been
thought through thoroughly.
In conclusion editor Dave Peterson took an action item to provide an
annex covering the whole process by enlisting the help of a few
#3 Matt Wakeley (HP) Comment titled: The Tape Profile should not
prohibit establish commands.
Dal Allan groaned, noting that this is the same argument that has been
rehashed many times. Dal argued that if people would only read the
document definition of prohibit this would not be a problem. George
Penoki agreed with Dal but sided with the letter ballot comment that
he felt that prohibited is too strong of a term. Bob Snively noted
that there are two parts to compliance. All required commands must be
implemented and all other commands must never be required. There was
some discussion of compliance testing.
Bob reiterated his goal that he doesn't want to have to consult
individual manuals to write a driver. He just wants to use the
compliant command list. Dave Peterson felt that limiting commands
exceeded the scope of the profile. The goal is to leverage existing
SCSI solutions to Fibre Channel. Rob Basham noted that the command set
on his Fibre Channel and SCSI drives will be the same. Rob's drives
will support every required command. He sees the list as a systems
house issue and is irrelevant to tape drives in the short term.
However it may become relevant in the future.
Dave questioned the relevance of this activity. Dal and Bob disagreed
that a common command set is necessary for interoperability which is
within the scope of the project. Dal Allan noted how difficult it is
to remove commands. There is substantial cost savings by reducing the
number of commands supported because it reduces the testing required
for proving compliance. Dave Peterson agreed but said this effort
belongs in the SSC. Rob Basham felt it was a secondary issue that
should not delay the profile. Matt Wakeley felt that this issue is not
transport specific and should apply to any transport therefore it is
not relevant to this group. Dal agreed that Matt would be correct if
this is a standard, but this is an interoperability profile so it is
an appropriate activity.
Rob Basham proposed the profile will only contain commands and
parameters that are required for compliance to the profile. This
proposal passed on a letter ballot vote16 to 3.
Matt Wakeley asked for a vote on a proposal to remove the tables that
contain the compliant commands, the tables 26 and 27, entirely. This
vote failed 2 to 12.
The editor was instructed to remove all of the commands that are
prohibited from the table and update statements about
#4. Matt Wakeley (HP) Comment (untitled) on alerting an initiator to a
CRN sequencing problem.
The problem occurs if the target is unable to get the initiator to
respond to a missing CRN. The conclusion was after RR_TOV to
explicitly log out the initiator.
Stewart Wyatt questioned the assumption that the target would retain a
command received out-of-order. Dale Lafollette replied that the target
was expected to execute the commands in order thought they might not
be received in-order.
#5 Charles Binford (LSI) CommentID 6. Class 3 and Link Control.
The note referred to in this comment suggests that an ACK should be
rejected in Class 3. A discussion followed about appropriate behavior
and confusion in other documents. Matt Wakeley proposed removing the
comment from profile and defer to FC-PH. This was accepted.
#6 Charles Binford (LSI) CommentID 8
Charles requested that the profile requesting text for clause 5.13
which is on sequence and exchange management. Previous versions of the
profile included text copied from the PLDA. The group had decided to
remove the text and refer to FC-PH. The group voted 9 to 0 to reject
the comment (Replacing text previously removed.) Note that Charles
Binford was not present to defend his comment.
#7 Charles Binford (LSI) CommentID 9 LPE/LPB should be I not P.
Stewart Wyatt noted that a footnote promotes this feature while the
table prohibits it. Bob Snively and Dale LaFollette argued that
feature is not useful and that the footnote should be removed. Matt
Wakeley was concerned about loops with non-tape devices which may need
this feature as he felt it put hosts in a no-win situation. A host may
need to use LPEfx which applies to all devices on the loop and may be
useful in some environments.
The question was put to a vote: Shall initiators be allowed to
initiate LPE/LPB? (Changes P to A) 11 yes 2 no. A second question was
voted on: Should the footnote be eliminated altogether? 5 voted yes
and 8 voted to keep it. A third vote was should the note be changed?
Approved 13 to 0. The note should be modified to say: Allowed so that
the initiator may manipulate non-tape devices.
#8 Robert Snively (SUN) CommentID 26. Incorrect value for FCP_TOV
Bob argued that the only reasonable use for FCP_TOV is as a polling
interval for REC.The group agreed and the editor was instructed to
remove item (a) "time FCP level information unit reply Sequences" from
clause 7.6. The group also agree to change timer name to REC_TOV to
emphasize its function.
#9 Bob Snively (SUN) CommentID 24. Problem with E_D_TOV definitions.
Matt noted some errors in Bob's comments which Bob accepted. E_D_TOV
definition is flawed since it doesn't consider delays in the loop.
(This needs to be fixed but is a project for another group.) Matt
Wakeley pointed out that a fabric attached initiator is entirely
unaware of the presence of a public loop that a target is attached to.
Bob proposed that the timer be large enough that the loop issues would
be covered. The comment was accepted with Matt's corrections and a
note that this solution needs to implemented until the underlying
problem are addressed by another group.
Bob was concerned about implementing multiple E_D_TOV timers to time
every outstanding sequence. A long discussion followed to convince
#10 Bob Snively (SUN) CommentID 25 Incorrect definition of RR_TOV.
Bob proposed setting RR_TOV to a constant value of 16 seconds. Rob
Basham said that RR_TOV has to be greater than E_D_TOV. Rob likes to
have the timers defined with respect to each other so that the order
in which they expire is always the same. This goal can also be
achieved if they are all defined by constant values. The proposed
value was questioned as being too short for some observed exchange
authentications to be completed as observed in the interoperability
tests. A question was raised about having multiple timers running when
a loop initialization occurs. Bill Martin noted that is unavoidable
since a fabric connected initiator will have an E_D_TOV time-out
running and will be unaware that the loop is initializing. A long
discussion followed about how the counters relate to each other. Then
Bob Snively lead an discussion to calculate the worst case value for
Stewart Wyatt pointed out that increasing RR_TOV requires a target to
keep more status assuming that status cannot be discarded until after
RR_TOV expires. Rob Basham gave an example of receiving many inquiries
from different initiators where most of them don't send a subsequent
command to confirm delivery of the previous status. Matt Wakeley
corrected the assumption that RR_TOV was the required time to retain
the status. The correct value is 3 times REC_TOV. Rob Basham told the
group that they needed to get used to the idea that targets could not
keep large amounts of data around for very long. The group decided to
separate the RR_TOV issue from holding status and consider only
exchange authentication for this discussion.
Dave Baldwin suggests a constant of 5 minutes since he has seen much
longer periods than 16 seconds. Jim Coomes thought that 5 minutes was
a reasonable value from his experience with disk drives. Note that
RR_TOV is a tunable parameter in Mode page 19. Dave's proposal was
#11 Bob Snively (SUN) CommentID 30 Note (Clause 8.2.1) is incomplete,
The issue is how a host determines that all of the data was
transferred with data overlay, since it cannot rely on counting the
bytes transferred and comparing the sum to the FCP_DL when data
overlay is allowed. Bob proposed that the note be changed to state
that the method to determine that all of the data is transferred is
beyond the scope of this profile.
Bob lead the group on a tutorial of how the host might make this
determination. One approach is for the initiator to depend on the
target to inform it that all of the data has been transferred when
error recovery occurs with the EMDP bit set. Bob thought the host
could do it but that it would be so difficult that it would rely on
the target. Rob Basham brought up the issue of read with SILI bit set.
In this case the target cannot inform the host if the transfer length
is different than what was requested. Bob corrected him by pointing
out that the FCP-DL always applies and provides the expected length.
If the target transfers a different amount it reports it as a residual
in the FCP_RSP. In this profile the host is required to make the
expected data transfer exactly equal to the FCP_DL field.
#12 Charles Binford (LSI) CommentID12 Limit data overlay to error
It appeared that Charles wanted to limit data overlay to error
recovery. Bob Snively felt that if it was allowed at all the target
could invoke it at its discretion.
6. T10 New Business:
Note the discussion of the FCP-2 reported earlier.
7. T11 New Business:
8. Review New Action Items:
The only new action item was for the editor to create an
The chairman noted that there will be no meeting in January. The
editor reported that he had reviewed the letter ballot comments and
had covered all of the comments in the meeting today that he believed
he needed guidance from the group on. He wanted to updated the profile
with the results of today's discussion and with the remaining letter
ballot comments. He felt like he could complete this by February's
meeting. A request was made for him to post the results two weeks
before the February meeting to allow the group time to review the new
draft before the meeting.
The meeting was adjourned about 6 PM.
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