Comment on proposal 09-357r0

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Wed Oct 7 08:33:15 PDT 2009


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Mark Evans recently posted proposal 09-357r0 (Relationship between low
power conditions and background tasks) and has asked for discussion of it
on the reflector. I'd like to offer my obervations.
I think the first four scenarios described in his proposal are sufficiently
described within the standards to arrive at these descriptions. The
descriptions are somewhat disk drive centric (e.g., giving special
consideration for START STOP UNIT and FORMAT comands) but I suspect these
same cases can be similary resolved for tape or other device classes with
similar device centric commands.
Scenario 5 proposes to add some mode bits to allow an initiator to choose
whether to let background tasks have priority over low power requests or
vice versa. I am not in favor of this concept.
Speaking for disk drives (other device classes may have a different
opinion), when we design background tasks they are for one reason -- to
increase the reliability of the disk drive. Let's be honest, background
tasks are a pain in the butt. They interfere with performance and power
savings, both of which are important to the customers. However the
customers also say that reliability is even more important than performance
or power savings.
My company will always want background tasks that ensure reliability to
take priority over low power conditions. All of my company's background
tasks fall into that category. Perhaps we can allow an initiator preference
to override background tasks that DO NOT enhance reliability. Then we end
up with a vendor specific interpretation of which background task might be
overridden and which ones are not, but I expect everyone will have
background tasks that are reliability related.
I think we are better off presuming background tasks are higher priority



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