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

Kevin D Butt kdbutt at us.ibm.com
Fri Dec 21 15:36:51 PST 2007


Formatted message: <A HREF="r0712213_f.htm">HTML-formatted message</A>

Geoff,
You are absolutely correct.
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-2869 / 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/ 
GBarton at overlandstorage.com 
12/21/2007 04:06 PM
To
Kevin D Butt/Tucson/IBM at IBMUS, t10 at t10.org
cc
Subject
RE: ADI - SMC tape alerts using ADI bridging (re proposal 06-420r2 and 
smc3r09)
Kevin, 
I suspect you are right. However, that still leaves problem if a 
implementer wanted to respond on a per initiator basis, as the SMC 
standard requires: smc2 clause 5.5.2 lettered list a) "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;". The 
same statement is in smc3r09 and in proposal 06-420r2 clause 5.4.3 with 
the "shall" changed to "should" or "may" depending on the state of the 
TAPLSD bit. 
Geoffrey L. Barton
Overland Storage
4820 Overland Ave.
San Diego, CA 92123
858 974-4586
gbarton at overlandstorage.com 
Kevin D Butt <kdbutt at us.ibm.com> 
Sent by: owner-t10 at t10.org 
12/19/2007 06:58 PM 
To
"Rose, Roger" <Rrose at tandbergdata.com> 
cc
GBarton at overlandstorage.com, owner-t10 at t10.org, t10 at t10.org 
Subject
RE: ADI - SMC tape alerts using ADI bridging (re proposal 06-420r2 and 
smc3r09)
I suspect that all implementers have only one set of SMC tapealerts and 
that they get cleared when the first initiator reads them.  I have not 
checked our implementation, but this is my guess since there is no way to 
communicate I_T nexus to the SMC device. 
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-2869 / 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/ 
"Rose, Roger" <Rrose at tandbergdata.com> 
Sent by: owner-t10 at t10.org 
12/19/2007 05:00 PM 
To
<t10 at t10.org>, <GBarton at overlandstorage.com> 
cc
Subject
RE: ADI - SMC tape alerts using ADI bridging (re proposal 06-420r2 and 
smc3r09)
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
----------------------------------------------------
Tiered Data Protection Made Simple
http://www.overlandstorage.com/
---------------------------------------------------- 



More information about the T10 mailing list