Advice about raw disk

[biokovo]

We have a few Linux+Oracle servers on Blade servers and MSA SAS storage.

I have never used a raw disk, and I am thinking to try it on this servers.

Is it any IO improvemant?

How to add a raw disk (I have no option (gray?!) to add raw disk in VM settings->Add disk...)?

Thanks

[jamesbowling]

From what I have seen, there isn't a huge difference in performance. I imagine it is really a personal choice. Do you already have a LUN carved out for the RDM? Is it already being presented to the host?

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[Rich123]

Take a look here:

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=101770...

Like James said, you need to have the storage carved out and presented first.

Rich

[biokovo]

Thanks. The problem was because option RdmFilter.HbaShared in host software advanced settings was checked, now is ok.

Is there any reason not to use the RDM?

If I will not use snapshoot is it better physical or virtual mode of raw disk?

[jamesbowling]

Do you plan on ever needing to vMotion the VM anywhere? If so, I believe you need to use Virtual Mode.

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[Rich123]

I have a few VMs that use RDM (physical). I can vMotion them. I can't snap them without shutting them down. As you've said, if you don't plan to snapshot, that may not be a big deal for you. I've found people get hooked on being able to snapshot because it gives a warm feeling of comfort that you can easily undue something that's gone wrong (if you have a snapshot).

vmware provides reasons to use RDMs as:

- If you plan to use VMs that will be in a Microsoft cluster

- If you plan to use SAN snapshots that needto see the raw storage

- If you plan to have big files

I'm actually looking at getting rid of my RDMs because of a backup solution we're considering. Vmware consolidated backup (VCB) ignores them and that's not what I'm looking for. I haven't been able to find a reason not to use them since the above three don't apply to me. If they don't apply to you either, I would stick with a virtual disk.

Rich