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SC3 versus SCSI_3 and
Can someone explain to me the difference between enabling the SC3 flag at the FA/HBA and enabling the SCSI-3 flag on the device? I understand the commands and syntax behind performing these tasks, and I understand what they're for and how SCSI-3 works. What I'm trying to understand what is enabled when SC3 is turned on on the Symm, versus what is enabled when SCSI_3 is set on the Symm devices. I'm looking for the technical detail as it applies to the protocol and the interaction between the host and the devices. To put it another way, if SC3 is turned on and SCSI_3 isn't what occurs and why, and if the SCSI_3 bit is set on the devices but SC3 is not enabled, same question. Thanks in advance!
Sam Claret
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May 25th, 2012 22:00
Hello
The difference is that the SCSI3 flag on the FA allows for the HBA to negotiate the SCSI3 protocol whereas the SCSI3 device flag – more commonly known as the PER flag allows for Persistent reservations on the device(s). Along with the SCSI3 FA flag there are 2 other flags that are normally required namely the OS2007 flag and the SPC2 flag.
If the SCSI3 flag is turned on and the PER flag is not then most standalone OSes will negotiate SCSI3 however certain features like for instance Windows 2008 clustering will fail.
If the PER flag is turned on but the SCSI3 flag is turned off then as the persistent reservation feature is a feature of the SCSI3 protocol but the communication is SCSI2 then the persistent reservation feature will not work. I cannot imagine a situation why you would enable the PER flag at the device level yet not turn on the SCSI3 flag at the FA level.
Thank you
Sam Claret
EMC Global Services
Support by Product - https://support.emc.com/products/
gboynt
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May 31st, 2012 12:00
Sam,
Thanks for the clarification! Awesome explanation....g.