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Julian,
I'm not sure I completely understand what you wrote, but if you're
suggesting that for a TMF that affects tasks from multiple initiators:
- Fast abort (early termination of data transfers) is used for the
sending
initiator.
- The existing 3270 abort mechanism is used with other initiators, with
the update that the TMF response does not have to wait for data
transfer
completion.
I think that suggestion is reasonable, and it actually helps with the
use
case that started this (3rd party initiator is dead). The draft text
would
need to change to allow this (right now it mandates fast abort in all
cases
if the key is negotiated to support it)
I'm not sure how target-scoped queues enter into this.
Thanks,
--David
----------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 176 South St., Hopkinton, MA 01748
+1 (508) 293-7953 FAX: +1 (508) 293-7786
[email protected] Mobile: +1 (978) 394-7754
----------------------------------------------------
________________________________
From: Julian Satran [mailto:[email protected]]
Sent: Friday, December 29, 2006 6:16 AM
To: Black, David
Cc: [email protected]; [email protected]
Subject: RE: [Ips] TMF text with updates
David,
My point was that we can solve the TM issue only for a single
initiator. So besides puting the burden on SCSI to cleanly finish other
and advise that fast solutions really work if there are no target scoped
queues there is little we can do. And if we limit ourselves to a single
initiator the multiple TM solution is a simpler (and basically does not
deviate from 3270). If you consider how software stacks are layered I
assume that some clever implementers have figured that already (and did
it).
Regards,
Julo
[email protected]
28/12/06 21:54
To
Julian Satran/Haifa/IBM@IBMIL, <[email protected]>
cc
<[email protected]>
Subject
RE: [Ips] TMF text with updates
I agree with Julian that we should avoid discussing "buffer
allocations" and
the like, even though we know that something like that has to
happen in at
least iSER implementations. A general discussion of "resources"
works.
> You could achive the same effect by issuing the TM command on
every affected connection.
Not for TMF's that affect commands from other initiators. Also,
asking the
target to coordinate receipt of the TM command on every
connection in a
multi-connection session is also a bit much.
> The third party story is even more puzzling as in order to
negotiate any of
> the new TM modes the taget will have to ascertain that all
other initiators
> support it. I fail to understand how would you handle
downgrading the mode
> for those that don't.
I think the target has to track this initiator by initiator, and
not issue the
new async message to old initiators. This increases the
importance of being
able to complete a TMF in the face of an uncooperative third
party "Legacy"
initiator.
> And if you don't downgrade why not state that fast-abort and
target scoped
> queues don't go together and simplify the mechanics to a
multiple issue TM.
This didn't parse for me - could you explain in more detail?
Thanks,
--David
----------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 176 South St., Hopkinton, MA 01748
+1 (508) 293-7953 FAX: +1 (508) 293-7786
[email protected] Mobile: +1 (978) 394-7754
----------------------------------------------------
________________________________
From: Julian Satran [mailto:[email protected]]
Sent: Thursday, December 28, 2006 5:32 AM
To: Mallikarjun C.
Cc: [email protected]
Subject: Re: [Ips] TMF text with updates
Mallikarjun,
I would consider the text:
c. MUST leave all active "affected TTTs" (i.e. active TTTs
associated with affected tasks) valid along with any buffer allocations
for the TTTs intact.
somewhat excessive as it relates too much to implementation. I
would rather say:
c. MUST leave all active "affected TTTs" (i.e. active TTTs
associated with affected tasks) valid.
and leave the buffer issue to the implementer (as I have stated
already on this list).
I also keep thinking (and mildly objecting to) that the whole
fast abort is excesively complex.
You could achive the same effect by issuing the TM command on
every affected connection.
The third party story is even more puzzling as in order to
negotiate any of the nem TM modes the taget will have to ascertain that
all other initiators support it. I fail to understand how would you
handle downgrading the mode for those that don't. And if you don't
downgrade why not state that fast-abort and target scoped queues don't
go together and simplify the mechanics to a multiple issue TM.
Thanks,
Julo
"Mallikarjun C." <[email protected]>
28/12/06 06:41
To
[email protected]
cc
Subject
[Ips] TMF text with updates
Attached is the latest text that incorporates David's proposed
enhancement. Please review and comment. Note especially two things:
new section 4.1.4 that summarizes generic implementation considerations
for both "clarified" and "updated" semantics, the changed text in 4.1.2
that says "MAY wait for ....target transfer tags.....from third-party
initiators" from the previous blanket MUST.
Mallikarjun
4.1.2 Clarified multi-task abort semantics
All iSCSI implementations MUST support the protocol behavior
defined in this section as the default behavior. The execution of ABORT
TASK SET, CLEAR TASK SET, LOGICAL UNIT RESET, TARGET WARM RESET, and
TARGET COLD RESET TMF Requests consists of the following sequence of
actions in the specified order on the specified party.
The initiator iSCSI layer:
a. MUST continue to respond to each TTT received for the
affected tasks.
b. Should receive any responses that the target may provide for
some tasks among the affected tasks (may process them as usual because
they are guaranteed to have chronologically originated prior to the TMF
response).
c. Should receive the TMF Response concluding all the tasks in
the set of affected tasks.
The target iSCSI layer:
a. MUST wait for currently valid target transfer tags of the
affected tasks from the issuing initiator to be responded to. MAY wait
for responses on currently valid target transfer tags of the affected
tasks from third-party initiators.
b. MUST wait (concurrent with the wait in Step.a) for all
commands of the affected tasks to be received based on the CmdSN
ordering. SHOULD NOT wait for new commands on third-party affected
sessions - only the instantiated tasks have to be considered for the
purpose of determining the affected tasks. In the case of target-scoped
requests (i.e. TARGET WARM RESET and TARGET COLD RESET), all the
commands that are not yet received on the issuing session in the command
stream however can be considered to have been received with no command
waiting period - i.e. the entire CmdSN space up to the CmdSN of the task
management function can be "plugged".
c. MUST propagate the TMF request to and receive the response
from the target SCSI layer.
d. MUST address the Response Fence flag on the TMF Response on
issuing session as defined in 3.3.2.
e. MUST address the Response Fence flag on the first post-TMF
Response on third-party sessions as defined in 3.3.2. If some tasks
originate from non-iSCSI I_T_L nexuses then the means by which the
target ensures that all affected tasks have returned their status to the
initiator are defined by the specific non-iSCSI transport protocol(s).
Implementation note: Technically, the TMF servicing is complete
in Step.d. Data transfers corresponding to terminated tasks may however
still be in progress on third-party iSCSI sessiosn even at the end of
Step.e. TMF Response MUST NOT be sent by the target iSCSI layer before
the end of Step.d, and MAY be sent at the end of Step.d despite these
outstanding Data transfers until after Step.e.
4.1.3 Updated multi-task abort semantics
Protocol behavior defined in this section MUST be implemented by
all iSCSI implementations complying with this document. Protocol
behavior defined in this section MUST be exhibited by iSCSI
implementations on an iSCSI session when they negotiate the
TaskReporting (section 9.1) key to "FastAbort" on that session. The
execution of ABORT TASK SET, CLEAR TASK SET, LOGICAL UNIT RESET, TARGET
WARM RESET, and TARGET COLD RESET TMF Requests consists of the following
sequence of actions in the specified order on the specified party.
The initiator iSCSI layer:
a. MUST NOT send any more Data-Out PDUs for affected tasks on
the issuing connection of the issuing iSCSI session once the TMF is sent
to the target.
b. Should receive any responses that the target may provide for
some tasks among the affected tasks (may process them as usual because
they are guaranteed to have chronologically originated prior to the TMF
response).
c. MUST respond to Async Message PDU with AsyncEvent=5 as
defined in section 8.1.
d. Should receive the TMF Response concluding all the tasks in
the set of affected tasks.
The target iSCSI layer:
a. MUST wait for all commands of the affected tasks to be
received based on the CmdSN ordering on the issuing session. SHOULD NOT
wait for new commands on third-party affected sessions - only the
instantiated tasks have to be considered for the purpose of determining
the affected tasks. In the case of target-scoped requests (i.e. TARGET
WARM RESET and TARGET COLD RESET), all the commands that are not yet
received on the issuing session in the command stream however can be
considered to have been received with no command waiting period - i.e.
the entire CmdSN space up to the CmdSN of the task management function
can be "plugged".
b. MUST propagate the TMF request to and receive the response
from the target SCSI layer.
c. MUST leave all active "affected TTTs" (i.e. active TTTs
associated with affected tasks) valid along with any buffer allocations
for the TTTs intact.
d. MUST generate an Asynchronous Message PDU with AsyncEvent=5
(section 8.1) on:
i) each connection of each third-party session that at least one
affected task is allegiant to, and
ii) each connection except the issuing connection of the issuing
session that has at least one allegiant affected task.
If there are multiple affected LUs (say due to a target reset),
then one Async Message PDU MUST be sent for each such LU on each
connection that has at least one allegiant affected task.
e. MUST address the Response Fence flag on the TMF Response on
issuing session as defined in 3.3.2.
f. MUST address the Response Fence flag on the first post-TMF
Response on third-party sessions as defined in 3.3.2. If some tasks
originate from non-iSCSI I_T_L nexuses then the means by which the
target ensures that all affected tasks have returned their status to the
initiator are defined by the specific non-iSCSI transport protocol(s).
g. MUST free up the affected TTTs (and STags, if applicable) and
the corresponding buffers once it receives the associated Nop-Out
acknowledgement that the initiator generated in response to the Async
Message.
Implementation note: Technically, the TMF servicing is complete
in Step.e. Data transfers corresponding to terminated tasks may however
still be in progress even at the end of Step.f. TMF Response MUST NOT
be sent by the target iSCSI layer before the end of Step.e, and MAY be
sent at the end of Step.e despite these outstanding Data transfers until
Step.g. Step.g specifies an event to free up any such resources that
may have been reserved to support outstanding data transfers.
4.1.3.1 Clearing effects update
Appendix F.1 of [RFC3720] specifies the clearing effects of
target and LU resets on "Incomplete TTTs" as "Y". This meant that a
target warm reset or a target cold reset or an LU reset would clear the
active TTTs upon completion. The TaskReporting=FastAbort (section 9.1)
semantics defined by this section however do not guarantee that the
active TTTs are cleared by the end of the reset operations. In fact,
the new semantics are designed to allow clearing the TTTs in a "lazy"
fashion after the TMF Response is delivered. Thus, when
TaskReporting=FastAbort is operational on a session, the clearing
effects of reset operations on "Incomplete TTTs" is "N".
4.1.4 Implementation considerations
Both in clarified semantics (section 4.1.2) and updated
semantics (section 4.1.3), there may be outstanding data transfers even
after the TMF completion is reported on the issuing session. In the
case of iSCSI/iSER [iSER], these would be tagged data transfers for
STags not owned by any active tasks. Whether or not real buffers
support these data transfers is implementation-dependent. However, the
data transfers logically MUST be silently discarded by the target iSCSI
layer in all cases. A target MAY, on an implementation-defined internal
timeout, also choose to drop the connections on which it did not receive
the expected Data-out sequences (section 4.1.2) or Nop-Out
acknowledgements (section 4.1.3) so as to reclaim the associated buffer,
STag and TTT resources as appropriate.
----- Original Message ----
From: "[email protected]" <[email protected]>
To: [email protected]; [email protected]; [email protected]
Sent: Wednesday, December 20, 2006 2:33:43 PM
Subject: RE: [Ips] Implementer's Guide - Task Management Issue
> Let's try this line of reasoning - the target issues the
Nop-Out, now
when
> can it free the resources? Answer:
> - The Nop-In response comes back, OR
> - The connection times out and is torn down.
> Now, what if the Nop-Out is not issued - what does the target
wait for
to
> free the resources? Answer:
> - The transfers complete, OR
> - The connection times out and is torn down.
> Those look similar enough at the target (the worst case is the
same -
the
> resources are tied up until an uncooperative initiator times
out) that
> I don't see the harm in allowing the early TMF return without
the new
> key. The clear distinction is that the first two bullets are
different;
> if the new key is not negotiated, the target has to wait for
the
transfers
> to complete; the new key and the Nop-Out are necessary to walk
away
earlier
> when the initiator involved is able to continue the transfers.
That got slightly twisted - what it should have talked about was
the
target
issuing the new Async Message and the Nop-Out response coming
back.
Thanks,
--David
----------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 176 South St., Hopkinton, MA 01748
+1 (508) 293-7953 FAX: +1 (508) 293-7786
[email protected] Mobile: +1 (978) 394-7754
----------------------------------------------------
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