SAS-2: Expander Notification of Temporary Shutdown proposal (T10/07-008r0)

George Penokie gop at us.ibm.com
Thu Dec 14 13:10:00 PST 2006


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At the last SAS meeting I briefly talked about a problem with code being 
loaded on expanders that causes the SAS network to go down without any 
warning. A proposal (07-008r0) has been posted that addresses this 
problem. If you are an expander type person and you allow code updates to 
your SES device you need to look at this as it will impact you. Send me 
any questions or comments you have on the proposal. A brief description of 
the problem and proposed solution follows:
Within the Service Delivery Subsystem in the SAS topology we have 
intelligent devices that will have to have their software updated. The 
software is updated by issuing WRITE BUFFER commands to a SES device 
within the expander device. When this occurs there will be a period of 
time while the flash is being written when the expander will not permit 
any traffic between it?s phys. This period of time can, depending on the 
implementation, take longer that a minute. After the code is written the 
expander will cause a reset sequence to occur on all it?s phys before 
allowing traffic to resume. 
Needless to say, this will cause timeouts at every layer of SAS for any 
operations outstanding at the time of the code download. This is a problem 
that can be handled within the current SAS and SCSI definitions by the 
application client/initiator device that issued the WRITE BUFFER command. 
However, any other application client/initiator device will not be happy, 
as any outstanding operations will without warning just disappear.
This proposal defines a NOTIFY (GOING OFFLINE) that expanders would use to 
notify all devices it is connected to that it will be temporarily (as in 
seconds) be shutting down all traffic. The NOTIFY is being proposed 
instead of a BROADCAST:
to allow the information to easily and quickly pass between zoning 
expanders; and
to allow notification of the expander going offline even when connections 
have been established.
Your request to upload a file or files to the T10 site has been accepted.
Your PDF file will be posted at:
   http://www.t10.org/ftp/t10/document.07/07-008r0.pdf
Bye for now,
George Penokie
Dept 9A8 030-3 A410
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208



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