ADC: WP bit in RMC logical unit subpage

Kevin D Butt kdbutt at us.ibm.com
Mon Mar 2 11:20:26 PST 2009


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ADC-3 dictates that the WP bit of the RMC logical unit subpage shall be 
cleared on unload.  Is the intent that the WP bit in the mode page is 
cleared so it will not be active for the next load.  In thinking through 
this scenario, I wonder if the wording in ADC has some issues that need 
resolved.  For example, which state does "unloaded" mean?
We need to be explicit about which state is meant.  Where this really 
matters is when does MAM not get a write protect?  I suspect the intent is 
unload state g.
To be explicit about scenarios where I think the standard is unclear, here 
is a list.
1) The volume is mounted and WP bit is set to one.  Then the volume is 
unloaded to unload state e).  A Write Attribute is attempted on MAM. 
Should there be a Check Condition (i.e., what is the value of the WP bit)?
2) After #1 the volume is then mounted and threaded and comes ready.  What 
is the value of the WP bit?
I think that the intent is to protect the currently mounted volume through 
the entire time that it might be altered.  Therefore, I think that MAM 
should also be protected until it is no longer accessible (i.e., until 
unload state is beyond f - that would g or h depending on technology). 
I also believe that the intent of the clearing the WP bit is to make sure 
that the next loaded volume is not inadvertently write protected.  This 
clearing would not apply to a volume that was unmounted to the hold point 
(i.e., MAM accessible) and then mounted again.	This volume should still 
be write protected.
Does anybody disagree with this?
Thanks,
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com



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