itmv2
Contributor
Contributor

Increasing size of RDM disk size in ESXi 6.7

I have a 4TB disk in an ESXi 6.7 server. It currently has a 3.55TB volume/vmdk file which is mapped to one of my VMs using RDM.

I have freed up the remaining space on the drive (85.03GB), and would like to use it to extend the existing 3.55TB volume. If I edit the disk settings in the VM it correctly shows the current size as 3.5546875TB. However the maximum size is shown as 85.03GB. It is thick provisioned.

If I want to extend the size of the disk to use the remaining available space, can I simply type 3.6397175TB into the box and click Save? (i.e. 3.5546875 + .08503)

Will this space be immediately visible/usable to the VM?

 

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9 Replies
a_p_
Leadership
Leadership

Can you please clarify/explain "... which is mapped to one of my VMs using RDM."?

A RDM is a pointer to a LUN/volume, and its size is that of the LUN/volume.

André

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itmv2
Contributor
Contributor

Apologies if I've used the wrong terminology - I'm not an expert in VMWare.

The volume is a vmdk file on the disk. I have created an RDM for it, and this RDM is allocated to the VM in question.

Does that make sense?

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ObjectifDubai
Enthusiast
Enthusiast

Hi 

The question is rather, why did you present an RDM to your machine, did you have a specific need? Because depending on the usefulness you make of RDMs, this can bring you some Constraint.

https://kb.vmware.com/s/article/1016106

https://docs.vmware.com/en/VMware-vSphere/6.7/com.vmware.vsphere.storage.doc/GUID-0114693D-94BF-4D0E...


In our infrastructure, we use RDMs for our SQL clusters.

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itmv2
Contributor
Contributor

The disk in question was previously the main data storage device on a physical server. When I virtualised the server I needed to retain the data content of the drive, so used RDM to map the existing device to the new VM.

I've now moved the VM to a new server, but have retained the same data storage device.

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itmv2
Contributor
Contributor

Apologies - I have confused matters. The 3.55TB storage is not actually mapped using RDM. There was an RDM file (on another disk on the server) with the same name, but it is not actually being used. So the storage is currently mapped as a normal VMFS datastore to the VM, and I would like to expand it to make use of the 80GB of free space on the same physical disk.

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a_p_
Leadership
Leadership

Now things start to make sense.

Most operating system (guest OS) will be able to use the newly provisioned space to increase a partition, or create a new one after increasing the virtual disk. However, in this case please remember that there may be other files on the datastore which need disk space. Also keep in mind that with allocation the complete physical disk space you will not be able to take VM snapshots.

With the sizes you mentioned, I'd actually keep things as they currently are.

André

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itmv2
Contributor
Contributor

As the disk in question regularly peaks at 95%+ usage I'm keen to exploit the 80GB of free space available, particularly as it will not be used for anything else. It's also not the main storage device on my ESXi server - the main drive has 40% free space.

As this is used for data storage only (not VMs or backups), if I simply overtype the size as previously noted, would the available space be usable to the associated VM? Would I need to use GParted to make it available after increasing the size?

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a_p_
Leadership
Leadership

How the guest OS partition can be resized depends on the guest OS itself , and the location of the additional disk space. In case of Windows, you can use the disk manager to increase a partition with adjacent free disk space.

André

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itmv2
Contributor
Contributor

The guest OS is Lubuntu (v20.04). 

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