ADI - SMC tape alerts using ADI bridging (re proposal 06-420r2 and smc3r09)

Rose, Roger Rrose at tandbergdata.com
Wed Dec 19 16:00:50 PST 2007


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Geoffrey,
I suppose I may be confused on which set of tape alerts.  (I tend to be
confused fairly easily.)
I haven't run tests on this either, but I doubt whether any ADI Bridge
drives cache the Library Log Sense data to allow per-initiator clearing.
There currently isn't any obvious mechanism to indicate that the Log
Sense data has changed and the cache needs refreshed.  
The technique you've described to pass the command through and update
the cache might be workable.  It appears to have an odd corner case:
If the Remote SMC Device Server clears Tape Alert bits upon sending them
to the bridge, then upon the next retrieval the bridge won't be able to
tell whether (a) the bits are still cleared from the last retrieval or
(b) the underlying condition has been cleared (e.g. by performing the
specified corrective action) and shouldn't be reported to other
initiators anymore.
If the Remote SMC Device Server doesn't clear Tape Alert bits upon
sending them to the bridge, then upon the next retrieval the bridge
won't be able to tell whether (a) the condition persists and should not
be reported again to initiators that have already seen it or (b) the
underlying condition was cleared and has actually occurred again.
I suspect that supporting per-initiator Tape Alert would require adding
another flag to Notify data Transfer Device or something along those
lines.	
-roger rose 
 Product Test, Tandberg Data 
________________________________
From: GBarton at overlandstorage.com [mailto:GBarton at overlandstorage.com] 
Sent: Wednesday, December 19, 2007 3:57 PM
To: t10 at t10.org
Cc: Rose, Roger
Subject: RE: ADI - SMC tape alerts using ADI bridging (re proposal
06-420r2 and smc3r09)
roger, 
I think what you are talking about is the TapeAlert for the DT device
(tape drive) as specified in ssc2 that the library can use to track
and/or report problems in it's tape drives. I am talking about the
library TapAlerts defined in smc2 and currently smc3 and referred to in
proposal 06-420r2. Currently, log page 12h TapeAlert Response Log Page
is not currently specified in smc2 or smc3. Rather, log page 2Eh
TapeAlert Log Page. If the host access to the library is through the ADI
bridge, the host (or hosts) can request log page 2Eh. There is currently
no mechanism using ADI bridging to clear the flags at the library on a
per I-T nexus basis, since the library has no visibility of the
initiator. The DT device (tape drive) can keep track of which initiators
have requested page 2Eh, but there is no mechanism to keep the tape
drive up to date on current tape alerts set, unless the DT device passes
the log sense command through the bridge (which will clear the flags in
the library) and intercepts the log page and updates cached values
accordingly. Is this being done by tape drives? I have not run an
experiment to find out. 
Geoffrey L. Barton
Overland Storage
4820 Overland Ave.
San Diego, CA 92123
858 974-4586
gbarton at overlandstorage.com 
"Rose, Roger" <Rrose at tandbergdata.com> 
12/19/2007 02:21 PM 
To
<GBarton at overlandstorage.com>, <t10 at t10.org> 
cc
Subject
RE: ADI - SMC tape alerts using ADI bridging (re proposal 06-420r2 and
smc3r09)
This is currently covered by ADC section 4.2.6 and ADC-2 Rev 8 section
4.6. 
>From ADC-2: 
4.6 TapeAlert application client interface 
The ADC device server supports a modified version of TapeAlert specified
in SSC-2. As supported by the ADC device server, the TapeAlert flags
represent states, and the state flags are not set to zero upon retrieval
of the TapeAlert Response log page (see 6.1.3). Instead, the state flags
are set to zero upon a change of the condition involved with the state
(see table 5). 
-roger rose 
 Product Test, Tandberg Data 
________________________________
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of
GBarton at overlandstorage.com
Sent: Tuesday, December 18, 2007 3:07 PM
To: curtis.ballard at hp.com; michael_banther at hp.com; kdbutt at us.ibm.com;
halvard.eriksen at tandbergstorage.com; PayneR at iomega.com;
Paul.Stone at Quantum.com; paul.suhler at Quantum.com
Cc: t10 at t10.org
Subject: ADI - SMC tape alerts using ADI bridging (re proposal 06-420r2
and smc3r09)
In reviewing Michael Banther's proposal for tape alert flag (06-420r2),
it occurred to me that there is a problem with SMC tape alerts in
general if ADI bridging is being used for host access to the library. 
smc3r09 clause 5.2.2 third paragraph defines deactivations for tape
alerts. Numbered list 1) states "after the TapeAlert log page is read.
The TapeAlert flags shall be deactivated on a per-initiator basis such
that active flags are available for other initiators; ".   
and in proposal 06-420r2 clause 5.4.4 last paragraph, the same statement
is made with "should" instead of "shall". 
Since a library device using ADI bridging is not aware of initiators,
the library cannot clear the flags on a per initiator basis. Does this
mean the DT device must cache the tape alert log page and keep track of
the reads of that log page? If so, how does the DT device know when to
cache a new page? And if the DT device handles the tape alert log page
on a per initiator basis, how does the library know when to clear the
flags? As far as I can tell, there is no mechanism to handle this. 
Even if proposal 06-420r2 is not incorporated into smc3, the problem
still exists. 
regards, 
Geoffrey L. Barton
Overland Storage
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