VMware Solutions Discussions

Cross-cluster and swap LUNs


Hi NetApp Community!  This is more of a VMware question, but I thought I would post it here too in case there were NetApp specific answers that I might not get from the VMware forums...

I've just recently aquired a NetApp FAS2240-2 (HA) for my datacenter.  I have had an engineer come out and install it and do some knowledge transfer, and now I'm ready to hit the ground running.  My first priority is to get my VMs off of local storage and onto the NetApp so I can really start getting the most out of vCenter.  I just have 2 quick questions:

First, I have a questions about LUNs, and how they work across ESXi clusters.  In my environment, I will have 2 ESXi  clusters of 3 machines each.  This is because Dell recommends not  putting processors of significant difference into clusters together,  even if you're using EVC, etc.  So, I will have 2 initiator groups, 1 per  cluster, and I will also have several LUNs for use as datastores  divided amongst my OS versions for maximum deduplication. My question is  whether to associate the 2 igroups with the same LUNs or to create  separate LUNs per cluster using 1 igroup per.  I am aware that I  cannot vMotion between clusters/igroups just like I can't vMotion across 2 stand alone hosts that are not  clustered.  I would have to shut down the guest and migrate both  host/cluster and datastore.  For the sake of simplicity and storage  efficiency (avoiding the additional snapshot overhead, etc), I would  prefer to point both igroups at the same LUNs.  Does anyone see any reason not to do this?

Secondly, I have questions about offloading the the VMs swap space in each cluster.  The idea is to create datastores where ESXi  swap will take place rather than having a swap file inside the VM  itself so that the swap datastores won't be deduped or  mirrored, thus saving space in my DR filer.  My NetApp engineer showed me where to  configure these settings in vCenter, but the way he explained it  working does not appear to be a best practice according to the  other articles I've read.  If I understood him correctly, he would have me  create a swap LUN per host and link that LUN to the given host ONLY  (through a separate igroup I think).  However, in the NetApp documentation and several  forums I have read, the best practice appears to be to create a swap  LUN that all hosts in a cluster share just like any other datastore.  NetApp doc TR-3749 seems to indicate that isolating the swap datastores per host  (using local storage or otherwise I guess) negatively impacts vMotion  times, even though it still works.  Is this how you guys are doing swap?

I'm using vCenter 4.1 and ESXi 4.1u2 (Dell) on all of the relavent hosts...

To illustrate my question, I want my environment to look like this...

Thanks, Joey



Hi Joey,

According to the SAN best practices TR which I will attach a link to it states the following:

When provisioning LUNs for access via FC or iSCSI, the LUNs must be masked so that only the

appropriate hosts can connect to the LUNs. With a NetApp FAS system, LUN masking is

handled by the creation of initiator groups. NetApp recommends creating an igroup for each

VMware cluster. NetApp also recommends including in the name of the igroup the name of the

cluster and the protocol type (for example, DC1_FCP and DC1_iSCSI). This naming convention

and method simplify the management of igroups by reducing the total number created. It also

means that all ESX Servers in the cluster see each LUN at the same ID. Each initiator group

includes all of the FCP worldwide port names (WWPNs) or iSCSI qualified names (IQNs) of the

ESX Servers in the VMware cluster.

As far as your second question that one may more tricky simply due to the paging and how much you are doing and how hard that might hit the filer, that one I may not be the best person to answer but it will require some testing most likely to see.

I will send the TR to you.

Hope this helps.


Thanks for responding Brian, but this really doesn't answer my question.  I already know how initiator groups work.  I have read the the document that you sent, and I have read the VMware document that it references, but neither addresses either of my questions directly.  The VMware document talks about higher level concepts rather than actual practical design, but there is a section on VMFS which discusses how that file system segregates and protects VM files, so that's encouraging.  I really don't see any reason why this wouldn't work, I just hate to put it into production without some kind of reassurance...