What is the use of LUN WWN? We usually use LUN ID (1-255) to present the LUN to the host. Where can we use LUN WWN?
What is the use of LUN WWN? We usually use LUN ID (1-255) to present the LUN to the host. Where can we use LUN WWN?
Hi Narendra
My understanding is that each HBA in the servers connected to storage has a WWN. A particular LUN can be assigned a WWN, so that a specific HBA can access a LUN, known as LUN masking. This technique is not so important if zoning is implemented in the SAN fabric.
David Floyer
Posted By:David Floyer| Fri Nov 05, 2010 12:49
Narendra, from what I recall, the WWN of a LUN can be useful to certain Operating Systems and especially some multipathing software. Typically the WWN of a LUN is not used by end users. LUN Masking is usually done by allowing the WWPN of a particular HBA/CNA to access a user defined set of LUNs. At least that's how we do it..
Posted By:Erik Smith| Fri Nov 05, 2010 01:38
Generally WWN of aLUN is used by Application software like Data Migration.base line is it is used by some operating system and some multipathing software ,as pointed by Erik
Posted By:DeepakP| Fri Nov 05, 2010 02:59
Does it not used to map to host WWN during LUN presentation in the back ground process? Because we will provide same LUN ID while presenting different LUNs to different hosts.
Can any one please explain me how the Communication happen between a LUN and the Host (Server OS)? From OS->Kernel->HBA->FC channel->Controller ports->Controller->LUN?
Can any one please point me to a doc which clearly explains the basics of SAN communication at the frames level?
Posted By:Narendra Kumar G| Sat Nov 06, 2010 01:00
Narendra, on the implementations that I work with, each storage port WWPN provides a set of LUNs (e.g. 0-255). Each of these LUNs corresponds to a unique device that is being presented on that storage port. Typically, each host that will access the storage port will be granted access to a subset of these LUNs. A storage administrator grants access to the LUNs by selecting the WWPN of the host port and then selecting the LUNs that the WWPN can access.
I am not an host OS expert, but from what I understand, from the host point of view, each time a new storage port is discovered a new target is created within the SCSI stack and the LUNs on that target are associated with that target. For example target 0 / LUN 0 might be associated with storage port 1 and target 1 / LUN 0 would be associated with storage port 2. Because of the target / LUN nexus, the WWPN of the device is not necessary to uniquely identify each LUN. Each OS has it's own way of tying the target / LUN instances to a raw device that is then presented to the user.
In regards to an end-to-end description of the life of an I/O.. About 10 years ago I worked with a group of people to try and do just that. I think when we were all done it came to over 1000 pages! Unfortunately most of the information in these documents is EMC proprietary and as a result I cannot share it. I only mention it to give you an idea of the magnitude of what you are asking.. One of these documents (the one that deals with just FC SAN concepts) has been made available for download and is now called FC SAN Concepts and Protocols. See http://www.emc.com/collateral/hardware/technical-documentation/h4331-networked-storage-cncpts-prtcls-sol-gde.pdf . It won't contain everything you are looking for but should get you closer to your goal.
Erik
Posted By:Erik Smith| Sat Nov 06, 2010 02:42
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