2012-04-18 08:06 AM
Is the LUN accessed over iSCSI or FCP? There can be a need for a "shared" LUN e.g. MSCS, it that still means that only one host has "full" access to the LUN at a time.
Sharing a LUN over NetApp Controllers is controlled with the cfmode, which is since a long time now set to: single_image
With single_image the two controllers provide access to the LUN's (over FCP, hence my question) over all available ports and paths. With the corresponding Multiüathing software on the host, the LUN can be accessed (mapped) over all possible paths and ports. Where some paths are otpimal and some are less optimal...
Hope this helps.
2012-04-18 08:15 AM
It is worth to mention that non-optimal paths (i.e the ones going through the partner controller & cluster interconnect) should not be used under normal circumstances - hence the ALUA multipathing concept.
IMHO in layman's terms it is really fair to say that on NetApp any LUN is (almost) 'exclusively' owned by a single controller at any given time (unlike some other systems, e.g. HDS AMS, where two controllers can actively serve the same LUN)
2012-04-18 08:29 AM
Good explanations on where the LUN is owned and proxy paths already... lun share is used to allow nas protocol access to a lun. For example, you can nfs mount a volume, then loopback mount a lun to get block access over nas. Not used often but it is there and really shows the true unified storage with all protocol flexibility.
2012-04-18 08:44 AM
Correct me if i am wrong. So you are saying it is possible to share the lun and the filers are in the cluster mode. Can you provide the commands that are needed to achieve this? BTW the LUNs are accessed over FCP.
2012-04-18 08:47 AM
In 7-mode and Cluster-Mode the LUN is owned by one controller, but is accessible by other controllers. In 7-mode it is a proxy path that isn't recommended unless there is a failover. In cluster-mode it is available on any of the nodes in the (currently) up to 4-node cluster. ALUA is key to getting the optimal paths. Even though owned by one controller, you can move the volume hot... in 7-mode intra-controller to another aggregate, and cluster-mode to any aggregate on any node (intra-controller or any controller in the cluster).
2012-04-18 09:00 AM
Being a novice, I would like to know the procedure(or the steps required) on how to achieve this?. I mean in the cluster mode. Would be of great help.
2012-04-18 09:13 AM
You can get to a lun on any path on either controller...the lun is owned by one controller but the igroup allow access on the local node and proxy on the partner node.