Physical drive mapping in ESXI

tom01 · 21 Mar 2020 at 16:57

Hi guys,

I have an ESXI server with two physical drives installed. The first one holds all my VM's and associated datastores for those. I want to use the second drive for additional data storage as and when required.

Annoyingly I had this working previously when I set it up with the VMware thick client but I can't work out how to do it on the v6.x web client.

Do I need to create a datastore on the 2nd HDD? It will used be used only for raw storage and I'll share it out over the network for other VM's to be able to read/write to when required, but primarily it will be one VM requiring usage.

Any advice would be greatly appreciated, I'm running ESXi v6.7

tom01 · 21 Mar 2020 at 17:02

Ok I think what I am after is Raw device mapping, can anyone give any pointers?

khrall · 21 Mar 2020 at 21:31

I'm assuming these are internal drives (SATA/SAS) connected to a simple controller.

If it's a standalone ESXi server (no vCenter):
1.) enter host IP address in your browser of choice
2.) log in with root account
3.) click on storage on left hand side
4.) click on devices
5.) click on rescan
6.) click on new datastore and follow the wizard.

If it's via vCenter:
1.) log into vCenter
2.) right click on host on left hand side
3.) click storage
4.) click rescan storage
5.) click new datastore and follow the wizard.

Then create vmdk's as required for your VMs on the new datastore.

RDMs are used for mapping to a SAN LUN and probably not what you want, but I could be wrong.

tom01 · 23 Mar 2020 at 16:41

Thanks

I managed to complete the RDM action, however a new problem I am experiencing is that the storage drive is only presenting to Windows as a 2TB drive (1.5 TB usage storage), despite being a 6TB HDD. I'm still researching this at the moment, there appears to be a previously known issue with older versions of ESXI where there was a 2TB limitation on VMDK files, however this should have been resolved in later versions.

I'm on a version (ESXI 6.7 with a VMFS6 datastore) which is reputedly not affected by this issue but for reasons I can't work out at the moment the issue remains. It's driving me insane!

Throrik · 23 Mar 2020 at 16:41

RDMs are also a bit old-school and not really recommended anymore unless you have very specific requirements. I work in a place which still heavily utilises them and they're a bloody nightmare.

Edit - with your reply:

VMFS5 supports greater than 2 TB disk size for RDMs in physical compatibility mode only. These restrictions apply:

https://kb.vmware.com/s/article/2009226

tom01 · 23 Mar 2020 at 19:41

Throrik said:
RDMs are also a bit old-school and not really recommended anymore unless you have very specific requirements. I work in a place which still heavily utilises them and they're a bloody nightmare.

Edit - with your reply:

VMFS5 supports greater than 2 TB disk size for RDMs in physical compatibility mode only. These restrictions apply:

https://kb.vmware.com/s/article/2009226

Thanks for your reply and the link, can I ask what is the best way to achieve my goal then if RDM is considered an old approach? I have installed a secondary HDD which I want to present to a VM as a logical drive so that I can store large amounts of data to it and make it accessible to other network hosts. However in an ideal world I want the data stored on it raw so that if I were to remove it I could simply re-insert and the data is there as was. I thought RDM Was the best way to achieve this?

The only other route that I can think of is to create a datastore on the secondary HDD, but that isn't quite what I am after if I have understood correctly.

Last option I guess would be to use a NAS, however I ideally I'm not ready to do that just yet, that's long term.

Throrik · 23 Mar 2020 at 21:05

There's no real difference in what you want these days between an RDM and an NFS Datastore, especially if it's not for huge amounts of production systems. At most if you replaced the hard drive or moved it somewhere you would simply need to rescan/remap the NFS Datastore.

Alternatively you could use a VVOL:

https://www.codyhosterman.com/2017/10/comparing-vvols-to-vmdks-and-rdms/

It really depends on what licensing you have, how much effort you want to expand etc, for me RDMs are not the best way to achieve a simple datastore of data.

Hellsmk2 · 31 Mar 2020 at 19:50

I might be asking the obvious, but why not just add it as another datastore, add some additional vmdks to an existing vm, and then create a file share from within the guest vm?