GregMeathead
Enthusiast
Enthusiast

Physical RDM LUN Mapping issue

I have created a iSCSI LUN, presented it to both of my ESXiin the cluster.

Now im trying to add it as a RDM to one of the VMs but I see the following issue:

Somehow i can only use ESXi local datastore as a LUN mapping destination (the oprion Store with Virtual Machine is greyed out). All of my VMs sit on NFS Datastores (that are presented to both ESXi.

So if i store LUN mapping on host ocal storage how will that affect HA, VMotion?

What will happen if host dies and VM moves to another one? The local store with mapping will dissapear too

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7 Replies
vmroyale
Immortal
Immortal

Hello.

You can't use RDMs with NFS datastores, as RDMs are only available for VMFS-3 volumes.  If you use the local datastore, then vMotion and HA aren't going to work.

What is the need for the RDM?

Good Luck!

Brian Atkinson | vExpert | VMTN Moderator | Author of "VCP5-DCV VMware Certified Professional-Data Center Virtualization on vSphere 5.5 Study Guide: VCP-550" | @vmroyale | http://vmroyale.com
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GregMeathead
Enthusiast
Enthusiast

For Exchange 2010 (OS is on NFS Datastore, and i need Log and DB partitions to be on RDM).

i have found this:http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=100185...

it pretty mucgh says:

The VMKernel routes physical mode SCSI commands directly over the RDM mapping without any modifications. The operation fails because the NFS protocol does not support SCSI commands over this interface.
When adding an RDM to a virtual machine hosted on an NFS datastore, select a VMFS Datastore for the RDM's pointer files to be located.

So, can i just create a iSCS VMFS datastore, present it to both ESX and use it ONLY for RDM Mappings? Ths should work, shouldn't it?

if thats OK way to do it, how big should this VMFS should be, it will be used only for RDM Mapping/

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vmroyale
Immortal
Immortal

So, can i just create a iSCS VMFS datastore, present it to both ESX and use it ONLY for RDM Mappings? Ths should work, shouldn't it?

if thats OK way to do it, how big should this VMFS should be, it will be used only for RDM Mapping/

Yes, exactly.  Create a VMFS datastore for this VM, and then vMotion and HA will work with the RDM.  The size of the VMFS volume will depend on if you intend to use snapshots on the RDM.  If so, size accordingly and maybe even for worst-case.

Brian Atkinson | vExpert | VMTN Moderator | Author of "VCP5-DCV VMware Certified Professional-Data Center Virtualization on vSphere 5.5 Study Guide: VCP-550" | @vmroyale | http://vmroyale.com
GregMeathead
Enthusiast
Enthusiast

OK, thanks

I may get NetApp SnapManager for Exchange later, but i dont be using VM SnapShots.

So, there realy should be no data on that VMFS volumes, as RDM Mapping are only a pointers, right?

I will have 2 RDM (1.5 TB for DB and 300GB for Logs), so if i create a 10GB VMFS only for the mappings, should that be OK? (i  guess i can always expand it anyway).

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vmroyale
Immortal
Immortal

You will need the VMFS to hold the VMDKs for the Exchange VM as well, so that will be additional space.  There is also the possibility of a vswp file, and if you intend to snapshot the VMs memory you will also need space for this.  So, size of Exchange VMDKs + (memory size x2) + free space as insurance would be a reasonable size, IFF you don't ever want to snap it.  You might want to consider physical compatibility mode for the RDM as well.

Brian Atkinson | vExpert | VMTN Moderator | Author of "VCP5-DCV VMware Certified Professional-Data Center Virtualization on vSphere 5.5 Study Guide: VCP-550" | @vmroyale | http://vmroyale.com
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GregMeathead
Enthusiast
Enthusiast

Exchange is already created, it sits on NFS Datastore, vSwap sits on another NFS datastore (designed to hold only vSwap files for all VMs). So this VMFS LUN will be used only for RDM Mapping files.

I will user Physical RDM Mode.

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GreatWhiteTec
VMware Employee
VMware Employee

Hi Greg,

You can do what was already mentioned. Not sure if you already mapped the Exchange LUNs via MS iSCSI inititator. If you did you will have to re-map them from snapdrive. SME works well with RDMs.

Note from experience - If you plan to use SRM at some point for DR, you would need to move your Exchange from NFS to VMFS datastore (same as your RDM pointers). Just something to watch for.

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