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
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@overlandstorage.com
| "Rose, Roger"
<Rrose@tandbergdata.com>
12/19/2007 02:21 PM
|
|
To
| <GBarton@overlandstorage.com>,
<t10@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@t10.org
[mailto:owner-t10@t10.org] On Behalf Of
GBarton@overlandstorage.com
Sent: Tuesday, December 18, 2007 3:07
PM
To: curtis.ballard@hp.com; michael_banther@hp.com;
kdbutt@us.ibm.com; halvard.eriksen@tandbergstorage.com; PayneR@iomega.com;
Paul.Stone@Quantum.com; paul.suhler@Quantum.com
Cc:
t10@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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