Why doesn't ESXi 5.5 support RDM?

[riahc3]

Is there a reason why ESXi 5.5 does not support RDM? A lot of people ask for it and use it so I have no idea why VMWare doesnt work on this feature to implement it and support it natively, at least from a software point of view

Thank you

[Linjo]

That is incorrect, vSphere 5.5 support RDM:s and have done so for a long time:

Create Virtual Machines with RDMs

// Linjo

[lakshya32]

Hi

Welcome to communities.

Its support , below is the documented kb.

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=101753...

[vThinkBeyondVM]

I daily use RDM in my test environment@ESXi 5.5. It is supported even on MSCS(Microsoft cluster service)

[riahc3]

What I ment by not being supported is that I cannot do it in vSphere Client.

It also disappears several times for me when I use a workaround....

[RichardBrown]

That just doesnt make ane sense

[riahc3]

What part doesn't? I followed this: http://forza-it.co.uk/esxi-5-1-using-raw-device-mappings-rdm-on-an-hp-microserver/ and while it works, in a few week, it suddenly disappears from My PC. I open Disk Management in WS2012R2 and it tells me I have to reinitialize my drive again, losing all my data. That's what I ment 🙂

[RichardBrown]

Ok... So an RDM is a raw Device Mapping and is a feature of VMware and has been for a long time all it does is point a guest to a disk adding a vmdk pointer. If the RDM is disconnecting from your vm there must be another issue like the path is lost but it's local right? have you checked to see if the RDM pointer still exists after it gets disconnected, you dont have any power saving features on your hosts causing them to hibernate do you and is the vm migrating to other hosts where the local storage isnt available? We use RDMs and always have the only issue i have experience is due to paths.

One question, if its local why use RDM's over vmdk?

[riahc3]

Yes, the path is local. Its directly inside the machine that is running ESXi. "have you checked to see if the RDM pointer still exists after it gets disconnected" Yes, the pointer does exist. "you dont have any power saving features on your hosts causing them to hibernate do you" Default WS2012R2. Shouldnt have any power saving features enabled. "is the vm migrating to other hosts where the local storage isnt available? We use RDMs and always have the only issue i have experience is due to paths." Describe a typical issue because of paths. I cant think of anything that can affect this. BTW, Ive done this 3 times and 3 times the ame thing always happens. "One question, if its local why use RDM's over vmdk?" Performance and S.M.A.R.T monitoring.

[riahc3]

I hope I explained everything correctly.

[Linjo]

Not sure if I understand you correctly, in the first post you wrote:

Is there a reason why ESXi 5.5 does not support RDM? A lot of people ask for it and use it so I have no idea why VMWare doesnt work on this feature to implement it and support it natively, at least from a software point of view

And at the same time you are using it extensively and know that its there but it seems that there is some issues in your environment?

Maybe you should post a new thread with this particular problem with your configuration including logs etc?

// Linjo

[riahc3]

No. Im using a workaround to make it work. AFAIK, ESXi 5.5 does not support it natively. My thread is about why doesn't WMWare implement it natively (even in a software mode) so it works quick and easy.

Posting it here will just get me a "This is not supported" answer.

[vlho]

Hi,

why VMware does not support RDM on local HDD?

Look here:

http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&docType=kc&docTypeID=DT_KB_1_1&e...

section Cause and beginning of Resolution

[Linjo]

You missed to mention the small detail that you are referring to locally attached disks, that would have been helpful...

I think the KB-is quite clear and it does not state that its not supported, its certain controllers that does not have the functionality needed to use with RDM.

Have you followed the instructions?

// Linjo

[riahc3]

Yup, I followed the instructions and it initially works, but then all of a sudden disappears for Windows and Windows tells me I have to reinitialize the disk...

Im doing this on a HP N54L

[Linjo]

Is your controller supported? I don't think the N54L is on the HCL.

// Linjo

[riahc3]

The odd this is that several N54L owners have gotten this to work. I was hoping that someone could shed a light... That or VMware implements a software solution.

[riahc3]

I think that even though certain controllers do not support it, VMWare should implement a workaround/software way to do it. You clearly see that there are methods to do it so maybe VMWare should also work on some way to do it.

[TomHowarth]

where did you read that ESXi 5.5 does not support RDMs. this is not true it does.  it is just that it is not used that often as the use cases for their utilization diminish, with improvements in the product

[riahc3]

http://kb.vmware.com/selfservice/search.do?cmd=displayKC&docType=kc&docTypeID=DT_KB_1_1&externalId=1... Here. There should be a software workaround avaliable.