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@us.ibm.com
http://www-03.ibm.com/servers/storage/


GBarton@overlandstorage.com

12/21/2007 04:06 PM

To
Kevin D Butt/Tucson/IBM@IBMUS, t10@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@overlandstorage.com

Kevin D Butt <kdbutt@us.ibm.com>
Sent by: owner-t10@t10.org

12/19/2007 06:58 PM


To
"Rose, Roger" <Rrose@tandbergdata.com>
cc
GBarton@overlandstorage.com, owner-t10@t10.org, t10@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@us.ibm.com
http://www-03.ibm.com/servers/storage/
"Rose, Roger" <Rrose@tandbergdata.com>
Sent by: owner-t10@t10.org

12/19/2007 05:00 PM


To
<t10@t10.org>, <GBarton@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@overlandstorage.com [mailto:GBarton@overlandstorage.com]
Sent: Wednesday, December 19, 2007 3:57 PM
To: t10@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@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


----------------------------------------------------
Tiered Data Protection Made Simple
http://www.overlandstorage.com/
----------------------------------------------------