Why Not Windows Dynamic Disks?

Question

CX3-20P SAN.

I see it in our Dell/EMC SAN docs, in our training materials -- EMC recommends against setting up the host disks/space as Windows dynamic disks.

Why?

We have a requirement that each Windows host have *one* drive letter pointing to the space on our CX3-20P SAN, but our LUNs are now hitting 2TB. And the NTFS limit is 2TB for any disk (other than GPT).

We had considered mounting a new LUN and making it a mount point under a folder in the drive letter with the original LUN -- thus letting us get past the 2TB limit.But the original LUN disk in Windows has to be a dynamic disk to allow this.

We have talked about GPT also -- are there any issues with GPT on a CX3?

What software, features, functions of the CX series won't work if we convert our disks to dynamic? Or to GPT?

Thanks!

Dana

dynamox · Answer

We had considered mounting a new LUN and making it a
mount point under a folder in the drive letter with
the original LUN -- thus letting us get past the 2TB
limit.But the original LUN disk in Windows has to be
a dynamic disk to allow this.

Dana,

where did you see this requirement that the disk has to be dynamic disk ? I've seen documents that explain how to use mount points with MS Cluster services, and you probably know that dynamic drives can not be added as cluster disk resources. So i am kind of curious where you saw that ?

dynamox · Answer

also some of your questions may be answered here:

Home > Support > Technical Documentation and Advisories > Host Connectivity/HBAs > Installation/Configuration

look for "EMC Host Connectivity Guide for Windows -- A25"

AranH1 · Answer

Dana,Using mount points does not require dynamic disks. If you read this somewhere it is wrong. I use mount points extensively in my environment and do not use dynamic disks at all. I also have many disks over 2TB and do not use dynamic disks. I prefer to use the GPT disks to achieve greater than 2TB LUNs. Dynamic disks in my opinion create limitations and I don't use dynamic disks for LUN expansion, so there is no need in my environment for dynamic disks. Just make sure you are on SP2 if using Windows 2003 and you should not have any issues with GPT disks.It won't matter to the array if you are using basic, dynamic, or GPT format for the disks. If you are going to use Replication Manager though, dynamic disks are not supported.Hope this helps,Aran

AranH1 · Answer

Unfortunately, no. The creation of a GPT disk can only be performed on a RAW disk with no partitions on it.

And the GPT format is supported by EMC software that interacts with the file system like Replication Manager. If you don't use any software like that then the disk format won't generally matter to the array. The array sees it all as blocks and is not aware of the files systems resident on each LUN.

DBrigham · Answer

Well, I went back and checked. I swear that I saw that requirement in the procedures for creating "mounted drives" under Disk Management. But I don't see it now!

So if we go with GPT, that causes no issues with EMC or EMC software?

Any nice simple way to convert a 2TB basic NTFS disk over to GPT with no data loss?????

Thank you (all)!!!

Dana

kelleg · Answer

Just a reminder as I still see that a lot of installations seem to overlook this until there is a performance issueglen

kelleg · Answer

Don't forget to consider the file-system offset - I believe that GPT disks need an offset just like NTFS disks do - do first rather than later - better performance.glen

AranH1 · Answer

Correct, but that is file system related not disk 'type' related. Whether it is a MBR (basic) disk or GPT disk you will still need to create the alignment offset for the partition in diskpart.

AranH1 · Answer

Definitely agree. That one little step gets overlooked a lot and has a significant impact on performance.

CLARiiON

Why Not Windows Dynamic Disks?

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