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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: iSCSI: problem with LUN discovery> -----Original Message----- > From: owner-ips@ece.cmu.edu [mailto:owner-ips@ece.cmu.edu]On Behalf Of > John Hufferd/San Jose/IBM > Y P Cheng, > OK, now I have detected an important communication problem here. What you > are calling a LUN is not what the rest of us folks (or at lest me) call a > LUN. <snip> <snip> Thank you for a nice summary of the definitions of LU and LUN. No, we did not have disagreement. It is only mis-communication. (If I did not real your email incorrectly.) LUN, the address of an LU, is embedded in an iSCSI command PDU or an FC command frame to direct a SCSI command to the LU. What confuses people is that the SCSI LU today is virtual and has nothing to do with real physical devices. The virtual to real mapping will be done by system administrator who reconfigures new and replaces bad SCSI devices. Each SCSI device in iSCSI should have a GUID. However, a physical device is not visible to an application. Software like Veritas adds one more layer of virtualization by taking the virtual LU's and making them virtual volumes. All I said was that the LUN needs not be unique world wide. An LU has its unique attributes that can be obtained by page 0x83h. A login or CONNECT discussed in another thread provides the TCP connection to reach an iSCSI node. The connection is used by the TCP/IP transport. Within an iSCSI PDU, an LUN is specified.
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