Fileserver data partition rdm or vmfs

[J-D]

Hi,

I want to put a fileserver in a VM attached to a SAN. The VM has a C-partition on a RAID1 Array on the SAN. I have a second RAID 5 array that I can use. I can make this second array a VMFS one or I can use it for a RDM.

The data-partition of the fileserver will be 400 GB. I had created a VMFS volume using default parameters and now it says the max size is 256 GB. Okay this makes sense to me, I'll have to reformat the VMFS volume with other parameters but I am wondering if I should do that, hence my post here.

Is RDM a better solution here? On the SAN I will use the same spindles/disks etc...

If I use RDM, will I still be able to use VMotion? My 2 ESX servers both have access to the SAN.

Any hidden dangers I should know?

What are you guys using for the datapartition of a VM'd fileserver?

Thanks in advance for any info.

J.

[VirtualNoitall]

Hello,

I would stick with VMFS. You get near native performance plus the benefit of an encapsulated disk drive. The only reason I would look at RDM would be for SAN specific snapshot\backup\? facilities that would require RDM.

[J-D]

Hi,

in a VMware document I found:

-

---

RDM is recommended when a virtual machine must interact with a real disk on

the SAN. This is the case, for example, when you make disk array snapshots or,

more rarely, if you have a large amount of data that you don't want to move onto

a virtual disk. It is also required for Microsoft Cluster Service setup. See the

VMware document Setup for Microsoft Cluster Service for more information.

---

We won't use SAN snapshot technology (was too expensive). But I am wondering if such a big disk on VMFS isn't more prone to corruption. I won't use VMware snapshots on this as this is purely data which I can backup nicely using the DataProtector agent in the VM.

Also when using RDM, I can assign this LUN to another Windows physical server if necessary.

What is the advantage of an "encapsulated disk drive"?

[VirtualNoitall · Accepted solution]

What is the advantage of an "encapsulated disk drive"?

for me it is portability. I can pick them up and drop them anywhere with little thought. If there is a performance issue I can pick it up and drop it onto another LUN, maybe on another SAN, with a different RAID config or number of drives. I feel like I have more control over it than with an RDM

You have mentioned a good advantage to using RDM. It really comes down to your needs. Everything being equal though I would take a VMFS hosted disk file over RDM. I don't have a vm drive as large as 400GB but I can tell you if there were corruption issues with large drives on vmfs this board would be up in arms.

Does that help?

[mreferre]

This touches on the RDM Vs VMFS ... among other things.

http://it20.info/blogs/main/archive/2007/03/11/4.aspx

My vote goes to VMFS.

Massimo.