Clariion Lun removal - Cluster

Hi Rahul,

If you have 3 hosts in a storage group, then any LUN assigned to this storage group will be available to all the hosts. Unfortunately nothing can be done about it, either through CLI or GUI. If you remove any LUN from the storage group, then all the hosts in the storage group will lose the LUN.

Hi Sushant,

Thanks for the reply !!

I know the way it works & I believe in what you say because I think the same , but somehow it doesn't make sense to me, why this should be the case. There can be situations like these where we might have to disable the lun from one host from the cluster.

There are numerous times I have done it on other arrays and it was a surprise for me when this situation popped up.

Thanks anyways !!

Rahul

You have to pre-plan for such a situation. In case you anticipate such a thing to happen, do not add the hosts to the same storage group. Create unique storage groups for each of the hosts. Add the luns to each storage group. If you do that, then you have the required level of control over the LUNs that are allocated to a particular host. Actually the concept of a storage group has a subtle aspect that the storage group will have a set of LUNs and Hosts. And all LUNs can be accessed by all the Hosts.

Anytime

I guess one is not so sure always about the way the design changes with the server teams. But personally,  I think it is more of a short coming then anything else with the feature within Clariion. This is a pretty normal scenario in other storage array where I can unmap the single lun from single storage array within a host/storage group which have the same function.

But I appreciate the time you took to write on this, thanks

Cheers !!

Rahul

As Sushant mentioend earlier that we can not either remove a particular lun for particular host either via CLI or GUI.

I just wanted to add up on that with a possible reason why to your query i.e AccessLogix. (if it is enabled)

- Access Logix is a licensed software package that runs on each storage processor (SP) in supported storage systems. Access Logix software lets multiple hosts share the storage system. It implements this storage sharing using Storage Groups.

- A Storage Group is one or more LUN swithin a storage system that is reserved for one or more hosts and is inaccessible to other hosts. Access Logix software enforces the host-to-Storage Group permissions.

- The Access Logix software is preinstalled on arrays at the factory.

On a CLARiiON storage system without Access Logix installed, or on a storage system where Access Logix is installed but not yet enabled, all CLARiiON LUNs are presented to all storage system ports. Any host that connects to the storage system will then have access to all of the LUNs on that storage system. In environments where multiple hosts attach to the storage system, this may cause problems. Windows systems may attempt to takeownership of LUNs belonging to other Windows systems, and Unix systems may try to mount Windows LUNs, for example. In addition to this, security is compromised because ofthe lack of access control.Access Logix solves these problems by performing LUN masking –it masks certain LUNs from hosts that are not authorized to see them, and presents those LUNs only to the server(s) which are authorized to see them. In effect, itpresent a ‘virtual storage system’to each host –the host sees the equivalent of a storage system dedicated to it alone, with only its own LUNs visible to it.

PS: The EMC Support Matrix lists which clusters are supported in the CLARiiON environment, and whether or not Access Logix is required, or permitted. As a general rule, Access Logix may no tbe required in direct-attach environments, where the clustered hosts are the only hosts accessing the storage system.

May be I am tasting Clariions after a long long  time and in between I tasted something else and i forgot how clariions tasted before But You are right in what you say and ofcourse there are tweaks to do what I want, but it was just a general query as to say , what if they include this feature ?

Thanks for your reply

Rahul

why are you surprised, it's been like this for more than 10+ years (going back to FC4500 and maybe earlier). The goal is to make it simple to manage, less tweaks = less errors. Even if you look at VMAX, they are now using storage group concepts where you are in the same boat if you need to remove single LUN from a single host. When EMC bought DG (Clariion) it's always been like that and apparently customers are ok with it otherwise numerous RFEs would demand a change. There are workarounds to make it work the way you want it to work.

Hi Ankit,

Thanks for chipping in and explaining the logic behind the AccessLogix. I perfectly understand the logic . I have been in this business for too long and when something of this sorts happen , you start comparing . Somehow today when someone asked me this question , I felt in comparision to other arrays where we have more flexibility on Lun level ( be it it's competitors) , Clariion with it's GUI looked like a step back.  It is not an Enterprise box, so there would be some limitations, but I think adding a feature where one could remove luns within a storage group (with multiple hosts ) for a single host does make sense , where we have migrations, test environments, node removal within cluster  and as I said , it is not the first time I have been asked to do something like this. But today it hit me, that we couldn't do it on Clariion due to the way it is designed and I was little surprised that I never realised it before.

Just to make things more clear, let me take an example where I have two nodes Server1 & Server2 in cluster but Server1 sees Lun 1,2,3,4 &5 and Server2 sees only Luns 1,2,4 & 5 for some server config requirements. In this case I will have to create two storage groups and map Luns individually because I don't want Lun3 to be masked to Server2. For me this creates an unnecessary overhead and while decommisioing , one can easily forget about these different storage domains with similar Luns. It is not flexible now either to add or remove luns, you have to work with two different storage groups and what if you have a 4 node cluster sharing luns , it can get complicated on the server side with the Host id numbers since i know some cluster config/server don't like different Lun id for the same Lun within cluster.

I wonder what would be the impact if we have a feature where one could remove storage on host level as well within clariions and not only at storage group level ? But that would mean changing the logic of it's working.

Thanks again for taking time to write !! Appreciate the time taken.

Rahul

Yeah , not a bad idea, I personally think , that it might make it more simpler to work

fill-out an RFE

Was your question answered correctly? If so, please remember to mark your question Answered when you get the correct answer and award points to the person providing the answer. This helps others searching for a similar issue.

glen