VMWare share SAN volume across datastores. Is it possible?

[Simo74]

I have recently inherited a VMWare setup with 2 ESXi hosts and an HP StoreVirtual SAN for storage.

On the SAN, there's a 2 TB volume which has been used to extend one of the datastores on VMWare however only 25% of this volume has been used for this. The remaining 75% is empty.

I now wanted to extend other datastores using the space on this volume but it will not show up as an available volume when trying to increase datastore size.

Basically my question is whether it's possible to share a SAN volume between datastores. I thought of reducing the SAN volume size but I feel it's too risky.

Before I start thinking of moving stuff etc. I wanted to know what I'm trying to do is possible.

I will also say that the reason for increasing the datastore size is for backup purposes. During backups the datastore must be big enough to accomodate snapshots etc.

Thanks in advance for any help.

[ThompsG]

Hi Simo74,

No you cannot do that. If you had a device/LUN that is empty then you could add it as an extent to an existing datastore to gain more space or if the array has space then extend the underlying LUN then extend the datastore.

Using space from one datastore (allocated or unallocated) against another datastore is not an option.

I agree that shrinking the LUN would be a risky option. Most arrays prevent this nowdays as determining which blocks are available for reclamation while not losing your data is probably not worth the risk of angry customers.

Best option would be to clear the datastore of VMs, then detach it, delete and recreate at the new size.

Kind regards.

[Simo74]

Thanks a lot for your reply.

Unfortunately I can't clear the datastore because VMs are running in it. I don't have space on the array to migrate them to another datastore either.

I don't understand why a datastore would own the whole space on a SAN volume even if it uses only part of it.

I'm now stuck with a datastore which is using 1.1TB on one SAN volume and 500gb (as an extension) on another volume which is 2TB and 1.5TB on this volume is therefore unusable.

I'll have to think of a way to reduce the size of the VMs and migrating them one by one on the limited space I have on the array. Then I might be able to clear the datastore as you said.

Thanks for your kind help.

[sgunelius]

This might be a stupid question, but could you temporarily add local storage to either of your hosts (maybe 2x2TB SATA), format that as VMFS, use Storage vMotion to migrate the VMs from the SAN-based datastore to the local datastore and once that volume is evacuated, reconfigure the SAN-based datastore to your liking.

Migrate the VMs back to the SAN-based datastore, unmount and delete the local datastore, then gracefully remove the temporary storage.

[Simo74]

Hmm.. yes I might be able to do this. I'll have to get the drives but I think it's possible. Thanks for the suggestion.

My client also has a VM with a secondary SQLServer installation that is not being used.. it's occupying 1TB .. I was thinking of doing a backup and then removing it. With that gone I then have an additional 1TB on the SAN to play around with and eventually I can then restore the VM from backup if needed.

Thanks so much for the time and help. Much appreciated.