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alexandru_ilie
Contributor
Contributor
‎06-21-2017 04:21 AM

Raw Device Mappings

Hello.

I have a question about Raw Device Mappings. I have never used this feature. What I would like to know is how the VM actually uses the Raw disk which gets assigned to it.

For example, if a RAW disk is assigned to a machine, will VmWare try to format that disk first in a format which VmWare understands?

In my case, I have an older windows server which uses some LUNs on a Storwize. I want to convert the system, which is physical, to a virtual server. The phisycal server has internal disks in raid 1. The internal disks are used for running the OS. However, due to the amount of data residing on the LUNs (on strowize), I was wondering if it is possible to assign the existing LUNs, used by the phicial machine, to the new virtual machine, as RAW disks. Will the existing data be kept on it or will it be deleted?

I think it will be deleted, because the RAW disk needs to be formated. But since I have never used it, it does not hurt to ask. Smiley Happy

Thank you!

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1 Reply
a_p_
Leadership
Leadership
‎06-21-2017 12:40 PM

I think it will be deleted, because the RAW disk needs to be formated

No, not at all. A Raw Device - i.e. the storage LUN itself - will not be touched, or modified by the Hypervisor (ESXi).

With creating an RDM, ESXi only creates a .vmdk mapping file which point to this LUN. The file system, and the data on that LUN are exactly the same, no matter whether the LUN is presented to a physical server, or as an RDM to a VM.

The only thing you need to ensure, is that the storage system is supported for the ESXi version you are going to use.

André

PS: Please ensure that the LUNs are presented to only one Windows OS (physical or virtual) at the same time to avoid possible data corruption!

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