[FAS3140]How to share a single LUN across two filers

[SOMU221087]

I have a requirement where in I should be able to share one single LUN on both filers. Is there a probability of doing this?  What does the lun share option do?

Thanks,

Somu

[peter_lehmann]

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.

[radek_kubka]

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)

Regards,

Radek

[SOMU221087]

Hi peter,

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.

Thanks,

Somu

[scottgelb]

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).

[SOMU221087]

Hi Scott

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.

Thanks,

Somu

[scottgelb]

The vol move command...really slick and works great.  Simple and no outage to move the lun.

[SOMU221087]

Because I am obviously not able to map a LUN on one filer to a igroup present on the other filer. That's the whole issue.

[scottgelb]

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.

[scottgelb]

By default when you create an igroup and map the Lun the paths on both nodes can see the Lun. So you only see local paths from mpio?

Sent from my iPhone 4S

[SOMU221087]

I created LUN on one controller(say filer-1) and mapped it to a local igroup present created on that controller but when I go to my other controller(say filer-2) I don't see that LUN and hence cannot map. Correct me if i am wrong, my understanding was each controller has different disks attached and LUNs created on one controller cannot be viewed on the other.

[scottgelb]

You don't have to map on the other controller and won't see it. Run igroup show -v on the controller with the Lun. And from the host you will see the Lun paths from both nodes

[aborzenkov]

You have to add to igroup on filer-1 initiators connected to both controllers (filer-1 and filer-2)

[scottgelb]

Works by default though with igroup and Lun map. Unless changed or port groups

[aborzenkov]

Just curious - which default? In CLI you have to list initiators explicitly. FileView last time I tried it presented only initiators connected to local filer. May be OCSM behavior has changed, but I do not dare to use it for configuration

[scottgelb]

When I create the igroup and map the Lin it is accessible on both controllers.

Sent from my iPhone 4S

[scottgelb]

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.

[SOMU221087]

Thank scott. That cleared my doubt over the "lun share" command usage.