danito
Contributor
Contributor

RAW DEVICE MAPPINGS

Hi to all,

Which is the difference in disks Raw Device Mappings, in configuration of the datastore.

Vmware ESX ask to me:

Select the datastore on which to store the lun mapping. You will use the disk map on this datastore to access the virtual disk.

STORE WITH VIRTUAL MACHINE.

SPECIFY DATASTORE.

Which is the diference between the two options?

Thanks.

Un saludo.
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7 Replies
jparnell
Hot Shot
Hot Shot

When you create a RDM, it creates a small file mapping file that points the virtual machine to the actual raw device or disk. This option is simply giving you the choice of where you want to locate this mapping file.

I would store it with the virtual machine for ease of management otherwise things could get messy if they are stored all over the place.

Texiwill
Leadership
Leadership

Hello,

As stated there is a .vmdk metafile that points to the location of the actual -rdm.vmdk file. The -rdm.vmdk file is not a real file but an entry in the VMFS metadata that points to the physical LUN used for the RDM. The placement of the .vmdk metadata file and the -rdm.vmdk in the VMFS structure can be with the VM or somewhere else. Just like a normal VMDK. However, the System LUN does not move just the metadata about that LUN does.

Best regards,

Edward

--
Edward L. Haletky
vExpert XII: 2009-2020,
VMTN Community Moderator
vSphere Upgrade Saga: https://www.astroarch.com/blogs
GitHub Repo: https://github.com/Texiwill
danito
Contributor
Contributor

Thankyou for the information.

Un saludo.
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vmjoe
Enthusiast
Enthusiast

Hello

I have to install several MS clusters (MSCS) across two boxes and I'll use RDMs. My questions is - where to store the mapping file? On the local VMFS (where the C: disk is) or on a shared SAN LUN?

I'm quite confused. There are recommendations to store it shared, but here's the clear advice to store it locally (on each ESX host of course, pointing to the same LUN):

http://www.vmware.com/pdf/vi3_301_201_mscs.pdf

Page 33: "In the Select Datastore page, select the local datastore, which is also the location of the boot disk, then click Next. This is the location where the RDM (mapping) is stored."

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vmjoe
Enthusiast
Enthusiast

No reply yet? Where do you folks store the mapping files in an MSCS-across-boxes configuration??

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MattG
Expert
Expert

Since MSCS clustered VMs boot disks must be installed on a local disk (non-SAN) to be a supported config, then it can't hurt to put the RDM there on the same local VMFS.

-MattG

-MattG If you find this information useful, please award points for "correct" or "helpful".
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jmmorrell
Contributor
Contributor

When using RDM's I am a little confused on the 2 datastore sections in the wizard.

The 1st datastore selection - *"select a datastore in which to store the files for the virtual machine." *This stores the VMX file & pointer that points to the RDM/LUN? Best practice is to store all of these in a central datastore for all VM's using RDM's?

The 2nd datastore selection is the one that is refered to in this post. Storing w/ the virtual machine or on a datastore. In the wizard it mentions that this is the LUN mapping to the disk. To me this sounds like the same.

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