Dynamic Disks on a SAN

[Lawrence Bowen]

Hi, a company that I work with has recently decided to upgrade all the SAN disks in their organisation to Dynamic Disks based on this article:

http://support.microsoft.com/?kbid=329707

The main driving force behind the decision was that it would provide a way to do LUN expansion at the server level. And also because the above article apparently recommends using Dynamic Disks for RAID5 SAN stripes.

I have read the above article and I do not understand it in the same way. Is it recommended to use Dynamic Disks on W2K SP3 SAN disks? If so why? If not, why? Is using Dynamic Disks a viable way to expand a SAN disk?

thanks! - lawrence bowen

[Mike Naime]

Everybody seems to be jumping on the storage virtualization bandwagon. I have seen demo's for the Storage controller level, the SAN switch level, and now the SERVER level.

One point from the link: Dynamic disks are not supported for use with Windows Clustering.

For me, if it's not a "cluster", it doesn't warrant SAN storage for us. YMMV.


For myself, I would prefer to let the EVA expand my LUN rather than have a OS level layer that is making bound volume sets.

If your customer will not purchase the newer technology, let them use this. This is probaly cheaper for them than to purchase new technology to do it at the hardware level. Make sure they have a GOOD backup strategy! and test it!

[Urban Petry]

When we first deployed W2K servers we were using dynamic disks as well. But that was only because at that time we didn't know about diskpart.exe and its possibilities and needed the "be able to grow a volume" functionality. Since then we reverted all the disks back to basic ones (good test for your backup btw.), because I cannot see any advantage of dynamic disks in this situation.

As long as your underlying hardware both supports fault tolerance and the possibility to extend an existing volume "in place" I can't see any need for dynamic disks with all their hassles (snapshots etc.).

With "in place" I mean the new space shows up as continous free space at the end of the old volume instead of being seen as a seperate, new "disk" (in our case, the EVA5000 can do it, but I bet almost all SAN storage systems should be able to do it)
Take a look at KB articles 325590 and 304736 (both referenced in the article you mentioned) for instructions on how to extend such a basic disk.

It is a misunderstanding that - regarding to your article - you should use dynamic disks on your SAN disks. What the article rather says is, that you should not have dynamic disks both on SAN disks _and_ locally attached disks at the same time. If you choose to use dynamic disks at all, either use them _only_ on local disks or _only_ on SAN disks. This is because of the internal LDM database that can become out of sync if the connection to the SAN disks is temporarily lost while the local disks can still be accessed. My summmary of that is: don't use dynamic disks at all and you won't have to care for these possible problems.

[Lawrence Bowen]

Thanks, but are you saying that you can extend a SAN disk at the controller level on HSG80 controllers, and then extend the partition on the OS level (W2K) using Diskpart.exe? Can anyone confirm that this works??

thanks - lawrence bowen

[Rob Buxton]

Not for the HSG80s.
The Virtualisation technology came out with the EVA which uses the HSV Controllers.

I don't know a way of dynamically growing a Raid Set using the older style HSG80s.

[Rob Buxton]

Just read a post in another thread, you can increase the size of a Raid Set with HSG80s by adding them to a concatset.
I've never tried this... the advice in the e-mail was read the manual and make sure you have a good backup!

[Andrew_168]

Hi,
Concat sets is one part of the answer, if you are not using Dynamic disks, then Diskpart found in the Windows resurce kit will expand a volume to fit the available space. Another HP product that is very useful is Virtual Replicator, costs a fair bit, but does work!