Snapshot Space usage for RDM disk

[sarpydog]

Dear All,

ESX Server can support VMDK Data Store, Compatibility RDM & physical RDM.

Is the disk speed comparability, physical RDM > Compatibility RDM > VMDK Data Store?

Compatibility RDM seems to can leverage virtualization Snapshot.

How does Compatibility RDM use snap spaces?

Thank you for any input.

Dennis Dai

[AndreTheGiant · Accepted solution]

Have a look at: http://www.vmware.com/files/pdf/vmfs_rdm_perf.pdf

Physical RDM are a little faster, but you cannot make snapshot on it.

Virtual RDM can create snap by creating a delta file into the VM folder, so you need space in this point to have the snapshot that grow up.

Andre

[depping]

Snapshot resides in the same folder as your VMs "vmx" file, so basically the working directory of the virtual machine.

Duncan

VMware Communities User Moderator | VCP | VCDX

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[a_p_]

There's another important point to think of when dealing with RDM's in virtual compatibility mode and snapshots.

To be able to take a snapshot, you have to make sure the VMFS datastore on which the virtual machine's base folder resides is configured with the appropriate block size.

Example: To be able to create a snapshot on a VM with a 700 GB RDM disk, your VMFS datastore needs at least a 4 MB block size!

André

[sarpydog]

Hi Andre,

Thank you for sharing good preformance doc.

Could you share me about adding delta sapces for Virtual RDM ?

Thank you,

Dennis Dai

[a_p_]

Dennis,

I assume your question:

Could you share me about adding delta spaces for Virtual RDM ?

referres to AndreTheGiant's post:

>Virtual RDM can create snap by creating a delta file into the VM folder, so you need space in this point to have the snapshot that grow up

If so, there's nothing you have to do manually. It just means, you have to make sure there's enough free space for snapshots (delta files) on the datastore where the VM's base folder is located.

André