FCP-2 public review comment resolution, changes to various documents
Robert Snively
rsnively at Brocade.COM
Tue Sep 11 07:01:18 PDT 2001
* From the T10 Reflector (t10 at t10.org), posted by:
* Robert Snively <rsnively at brocade.com>
*
To: T11, T10
From: Bob Snively
Date: September 10, 2001
Subject: Meeting resolving FCP-2 public review comment
INTRODUCTION:
A public review comment was received on FCP-2. The
comment indicated that early implementations of
FCP-2 tape environments were unable to continue
normal operation after certain induced errors. Review
of these recovery failures is still in progress, but
appears to be related to the execution of PLOGI
during the recovery process. The PLOGI resets the
tape drive's mode pages, making normal continuation
impossible.
The resolutions below summarize the changes in various
standards required to assure proper continuation of
tape operations in the presence of certain types of
errors.
RESOLUTION:
FC-FS
The document will recommend that PLOGI not be used
unless re-authentication after a temporary loss
of a link is unsuccessful.
FC-MI
The document will require that PLOGI not be used
unless re-authentication after a temporary loss
of a link is unsuccessful.
FC-DA
The document will require that PLOGI not be
used unless re-authentication after a temporary loss
of a link is unsuccessful.
SSC-2
The document will provide requirements on
mode pages and other mode select parameters that
will allow continued normal operation after a
reset. Recommendations will be made about the
behavior of mode pages and mode select parameters.
The recommendations will encourage saveability.
In addition, the definition of current and default
parameters will allow for the properties of the
tape that is loaded.
Note that some implementations of tape drives and host
adapters may be affected by these modifications.
No changes are required for FCP-2.
DISCUSSION AT THE MEETING:
1) Testing status
Roger Cummings presented testing status on the
study of the FCP-2 ballot problem.
The good news:
PLOGI causes backup jobs to fail by
resetting mode pages in mid-media.
Unplug and replug also mostly kills the backup.
The bad news:
We know almost nothing new.
None of the 3 recently received FC tape
drives, but none of them are ready for
prime time. None have yielded results
in which they have confidence. None will
support their standard acceptance test.
New test case:
Unplug receive side of tape drive only.
In point-to-point
4 out of 4 HBAs produce PLOGI at some
point in the loop reinitialization process.
Fabric
Tape drive issues successful FLOGI and
recovers.
The situation is frustrating.
They need more FCP-2 compliant equipment (HBAs and
tape drives)
Recommendations:
End consideration of unplug/replug case.
Accept Charles Binford's suggestion from
last time of a bit in Process LOGI to
select FCP behavior (i.e. no reset actions
from link-level events).
Add a note to FC-FS about the dangers of
PLOGI during "normal" fabric operation,
proposing the use of PDISC instead.
2) Discussion:
Dave Peterson:
Suggests the problem is HBA configuration
verification failures.
There was general agreement that HBAs should
not be performing PLOGI under the conditions that
have been identified. FC-PLDA, FCP-2, and other
documents indicate that authentication should not
use PLOGI.
However, because there is an installed base of
HBAs that do perform PLOGI, previous tape drives
have explicitly ignored PLOGI with respect to
resetting the mode pages and in fact leave the
state of the media and mode pages unchanged.
Those more up-to-date tape drives that correctly
implement the resetting of the mode pages are
caught by the legacy HBAs' behavior.
3) Proposed solutions from the committee:
FC-FS and FC-MI shall be changed. FC-FS will
recommend that PLOGI not be used unless
re-authentication is unsuccessful. FC-MI and FC-DA will
require that PLOGI not be used unless re-authentication
is unsuccessful. That will result in this
restriction being tested by SAN Mark tests.
Saved mode pages would be required. Requires
changes to both the application (to set the
save bit) and to the drives (to provide saved
pages). Some of these may also reflect into
some driver stacks. To find the parameters automatically
without using saved mode parameters may require
examining the tape at BOT. This would go in
SSC-2 and maybe in FC-DA.
The tape drive's "default parameters" should probably
reflect the actual present media installed. This
requires changes to the present tape and SSC-2.
If BOT access is required, this is a multi-minute
impact on the back-up process. The preferred
mechanism is to use saved parameters.
It is really key that parameters that can only be
established at BOT be remembered one way or another.
Later parameters (block length and others)
may be lost at the time of a reset. Notification
is provided by Unit Attention. Note that this is
still not much help, compared with saved parameters.
This makes recovery vendor specific.
Note that SSC-2 will have to include text that clarifies
that the block descriptor and the device specific parameter
(which SPC-2 defines as always "current") really means
that the value at the time of the reset must be
maintained.
Note that different mode sense pages may require special
reminders, especially with respect to partition and
device configuration pages.
Some tape vendors may be unhappy with this. Applications
may have to be tolerant of (if not happy about) devices
that cannot save pages.
It may be acceptable to create a "saveable" that is
saveable across resets, but not power-down.
4) Action items:
All participants to review the proposed approaches.
Robert Snively to prepare draft of public review
comment response for review by all participants.
Roger Cummings accepted an action item to create
appropriate text for FC-MI, FC-FS.
Dave Peterson accepted an action item to include the
proper concepts in FC-DA and in SSC-2.
ATTENDEES:
Robert Snively
Roger Cummings
Ken Moe
Kevin Butt
Bob Nixon
Dave Peterson
Rob Elliott
Ralph Weber
Erich Oetting
Paul Suhler
Bob Snively e-mail: rsnively at brocade.com
Brocade Communications Systems phone: 408 487 8135
1745 Technology Drive
San Jose, CA 95110
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