RAW disk vs RDM (Raw Disk Mapping)

[cave35]

Hi,

First time post and first time ESXi user.

I am trying to set up FreeNAS in ESXi 6.7U2. I am not able to pass through the HBA as recommended so I decided to try RAW disks. But I am confused as to what the differences are between a RAW disk vs the Raw Disk Mapping. Searching for RAW disk on ESXi invariably returns Raw Disk Mapping, which requires up going to the shell and making changes there. I am fine doing that if necessary. But without doing any of these, when adding a disk to the VM Guest, there is a RAW disk option from the drop down list, in addition to New, and Existing. And from there I can actually see the drives that I want to use. And FreeNAS doesn't complain at all and even the smartctl can see all the drive info, including models and SATA info. The only things it can't do is reading the smart status of the SATA drives. So the question is, what is the difference between this RAW disk option compared to the RDM option?

The system I am running:

Dell R510

64GB ECC RAM

H200 in IT mode

5x 4TB Seagate SATA drives as storage drives

1x 160GB drives for ESXi

All drives hang off the H200 and hence can't use PCI passthrough of the H200 for FreeNAS.

Thanks and look forward to your help.

[Dashers]

Pretty sure it's the same thing, just one through the UI - not an approach I've ever tried, maybe it's fairly new.

Either way, I'd probably suggest going with a physical rdm instead of a virtual rdm for NAS usage.

[daphnissov]

The difference between a raw device and an RDM are couple. But the biggest thing in your case is that your disks are local and note remote. Therefore, what you're talking about is raw disk presentation where there is no abstraction layer between the physical and virtual. The VM has low-level access to the disk devices themselves including the geometry. RDM is for presenting a remote extent (usually an abstraction of multiple physical disks) to a VM with that same level of underlying visibility.