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Are Spanned VMFS Datastores 'Safe' for production environments?



I'm a newbie to this forum, so I applogize in advance if this has been covered before.

I have a Fiber Channel connected FAS2040A and I need to present an 8TB volume to Windows Server 2008 for a Radiology Archive application

The agg consists of 10 2TB SATA drives in a RAID-DP configuration with 2 spares.

The server is running ESXi 4.1

The host O/S is Windows Server 2008

My intent was to present an 8TB LUN to ESXi and finally to the Windows 2008 virtual machine.

I was unaware of the 2TB limitation imposed by VMFS on its datastores.

The question at hand:

Are Spanned VMFS Datastores 'safe' to use in a production environment?

Both the Archive software vendor and I agree that Microsoft Dynamic Volumes are not a good soultion.

(He is currently dealing with a corrupted Microsoft Dynamic Volume at another customer's site).

We currently do not have a CIFS license for our FAS2040A system, that could be another option, but other issues then creep into the mix.

The vendor still requires Direct Attached Storage for 12-18 months worth of images and there are performance implications of Network, etc.

Bottom Line:

Has anybody had success/problems/issues/concerns with multi-extent VMFS volumes?

Thank you in advance for your comments!


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I'm guessing you probably wanted to start a "discussion" on the forum.  That is probably easier than a "document" (at least I think this is what you produced... I'm no power user here either).  In any case, is there any reason why you haven't considered an iSCSI volume? 

I sort of have to wonder, based on experience, if you are really going to have luck running this as a VMWare instance.  I realize that policy often dictates above common sense and that VMWare is often implemented as some sort of universal fix for high availability, but data volumes of this size that require some level of performance can be very problematic in virutalized environments.  Even the fact that you have the disk spec'd to just barely meet your size needs shows that you may very well run into performance problems if the archive is under any type of load.  Backup of 8TB of data on a regular basis is also no small feat and will put a significant load on the few disks that you have. You will probably get 50MB/sec and that makes for a long backup window.  8 SATA "data" disks are going to be slow as sirup and if you are running the rest of your VMWare setup on the same disks, you are on a painful road if you expect any sort of load on this solution.

I didn't get into spanned Datastores, but it sounds like a hack compared to one iSCSI/FC (normally the iSCSI license is free or almost free) LUN of 8TB (or some split-up version with mountpoint disks per directory... ).

Perhaps someone else with experience in this type of solution can be more specific, but I see some general architectural problems here and thought I'd share.

In any case, good luck.

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