Category Archives: SAN

Shared Virtual Disks in Windows Server 2012 R2 Hyper-V Maximizes TCO/ROI

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One of the great additions to Hyper-V in Windows Server 20012 R2 are shared virtual disks. TechEd 2013 is disclosing a lot of new and improved features and this is one of them!

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This single feature brings benefits to me I can use to solve business issues today:

Ease of guest clustering

How easy is it? Look at this:

New-VHD -Path C:ClusterStorageVolume1Shared.VHDX -Fixed -SizeBytes 30GB

Add-VMHardDiskDrive -VMName Node1 -Path C:ClusterStorageVolume1Shared.VHDX -ShareVirtualDisk

Add-VMHardDiskDrive -VMName Node2 -Path C:ClusterStorageVolume1Shared.VHDX –ShareVirtualDisk

That’s it, basically. No fabrics to extend to the guest, no vFC  needed. In simplicity it looks a lot like SMB 3.0. A major improvement.

To the guest the shared storage has become abstracted

With a shared VHDX I get mobility and flexibility I’m used to with VHDX files & virtualization. FC, iSCSI, SMB3.0, Storage Spaces, PCI Raid, Share SAS, it all doesn’t matter what happens to the underlying storage infrastructure when doing guest clustering in this way.That’s sweet!

Fast Backups

We have a lot of large size LUNs. 2-16TB. We want to virtualize all of these as the speed of backing up these large VHDX file  a LOT better than backing up a LUN with millions of smaller files. But when we need high availability we have to go for vFC, iSCSI and don’t get that benefit.  Yes we can also use SMB3.0 already gave us a helping hand (SQL Server guest clustering if you don’t or can’t do “Always On”) in some scenarios but it’s not the major storage deployment out there (not yet) AND we’re talking about file server workloads. Now with shared VHDX we can have our cookies and eat it to. Or better 2 cookies!

Conclusion

This just rocks. My live just got better and easier. So can yours. Moving to Windows Server 2012 (R2) is all that’s needed. For more information look here at Application Availability Strategies for the Private Cloud (Speakers: Jose Barreto, Steven Ekren)

Dell Storage Forum 2012 Paris – Fluid Forward Think Tank

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Thanks to some great people at Dell in Germany (yes, you Florian), Belgium and of course Alison Krause (@AlisonatDell), Maryna Frolova  (@MarineroF) and Stephanie Woodstrom I got invited to attend the “Fluid Forward Think Tank” at the Dell Storage Forum in Paris.

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We had a healthy variation in customers, partners, consultants and DELL employees discussing various aspects of IT related to storage. The task of herding the cats fell upon the shoulders of Simon Robinson (@simonrob451) who’s an Analyst and VP at 451 Research, a firm that deals with storage and information management. I for one think he did so brilliantly. This interactive discussion was streamed live and if you missed it you can click on this live stream link to look at our ramblings 🙂

I had to pitch some of my dreams of leveraging al the new mobility features as well as the high to continuous available that is being enabled with Windows Server 2012 Hyper-V on inherently unreliable components what opportunities these present to us customers and storage vendors.

Here’s the gang around the table:

It was a fun, educational discussion as the mix of backgrounds, industries, job functions was diverse enough to address all sides of the storage story, the good, the bad and the ugly. We gave them some food for taught I think. Well the folks at DELL can now take this back to Austin and reflect on it all. If need be, I’ll drop by some day to provide some feedback and remember @WarrenByle I ‘d like to try out that STI of his Winking smile  After an interview I ran of to a Compellent customer panel to learn something and provide some feedback on our first experiences.

Migration LUNs to your Compellent SAN

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A Hidden Gem in Compellent

As you might well know I’m in the process of doing a multi site SAN replacement project to modernize the infrastructure at a non disclosed organization. The purpose is to have a modern, feature reach, reliable and affordable storage solution that can provide the Windows Server 2012 roll out with modern features (ODX, SMI-S, …).

One of the nifty things you can do with a Compellent SAN is migrations from LUNs of the old SAN to the Compellent SAN with absolute minimal downtime. For us this has proven a real good way of migrating away from 2 HP EVA 8000 SANs to our new DELL Compellent environment. We use it to migrate file servers, Exchange 2010 DAG Member servers (zero downtime),  Hyper-V clusters, SQL Servers, etc. It’s nothing less than a hidden gem not enough people are aware off and it comes with the SAN. I was told that it was hard & not worth the effort by some … well clearly they never used and as such don’t know it. Or they work for competitors and want to keep this hidden Winking smile.

The Process

You have to set up the zoning on all SANs involved to all fabrics. This needs to be done right of course but I won’t be discussing this here. I want to focus on the process of what you can do. This is not a comprehensive how to. It depends on your environment and I can’t write you a migration manual without digging into that. And I can’t do that for free anyway. I need to eat & pay bills as well Winking smile

Basically you add your target Compellent SAN as a host to your legacy SAN (in our case HP EVA 8000) with an operating system type of “Unknown”. This will provide us with a path to expose EVA LUNs to our Compellent SAN.

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Depending on what server LUNs you are migrating this is when you might have some short downtime for that LUN. If you have shared nothing storage like in an Exchange 2010 or a SQL Server 2012 DAG you can do this without any downtime at all.

Stop any IO to the LUN if you can (suspend copies, shut down data bases, virtual machines) and take CSVs or disks offline. Do what is needed to prevent any application and data issue, this varies.

What we then do is we unpresent the LUN of a server on the legacy SAN.

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After a rescan of the disks on the server you’ll see that disk/LUN disappear.

This same LUN we then present to the Compellent host we added above.

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We then “Scan for Disks” in the Compellent Controller GUI. This will detect the LUN as an unassigned disk. That unassigned disk can be mapped to an “External Device” which we name after the LUN to keep things clear (“Classify Disk as External Device” in the picture below).

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Then we right click that External Device and choose to “Restore Volume from External Device”.

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This kicks off replication from the EVA LUN mapped to the Compellent target LUN. We can now map that replica to the host as you can see in this picture.

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After this rescan the disks on the server and voila, the server sees the LUN again. Bring the disk/CSV back online and you’re good to go.

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All the downtime you’ll have is at a well defined moment in time that you choose. You can do this one LUN at the time or multiple LUNs at once. Just don’t over do it with the number of concurrent migrations. Keep an eye on the CPU usage of your controllers.

After the replication has completed the Compellent SAN will transparently map the destination LUN to the server and remove the mapping for the replica.

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The next step is that the mirror is reversed. That means that while this replica exists the data written to the Compellent LUN is also mirrored to the old SAN LUN until you break the mirror.

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Once you decide you’re done replicating and don’t want to keep both LUNs in sync anymore, you break the mirror.

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You delete the remaining replica disk and you release the external disk.

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Now you unpresent the LUN from the Compellent host on your old SAN.

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After a rescan your disks will be shown as down in unassigned disks and you can delete them there. This completes the clean up after a LUN migration.

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Conclusion

When set up properly it works very well. Sure it takes some experimenting to deal with some intricacies, but once you figure all that out you’re good to go and are ready to deal with any hiccups that might occur. The main take away is that this provides for minimal downtime at a moment that you choose. You get this out of the box with your Compellent. That’s a pretty good deal I say!

So as you can see this particular environment will be ready for Windows Server 2012 & Hyper-V. Life is good!

Some SAN Storage Fun

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At the end of this day I was doing some basic IO tests on some LUNs on one of the new Compellent SANs. It’s amazing what 10 SSDs can achieve … We can still beat them in  certain scenarios but it takes 15 times more disks. But that’s not what this blog is about. This is about goofing off after 20:00 following another long day in another very long week, it’s about kicking the tires of Windows and the SAN now that we can.

For fun I created a 300TB LUN on a DELL Compellent, thin provisioned off cause, I only have 250 TB Smile

I then mounted it to a Windows 2008 R2 test server.

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The documented limit of a Volume in Windows 2008 R2 is 256TB when you use 64K allocation size. So I tested this limit by trying to format the entire LUN and create a 300TB simple volume. I brought it online, initialized it to an GPT disk, created a simple volume with an allocation unit size of 64K and well that failed with following error:

Failed Format300TB

There is nothing unexpected about this. This has to do with the maximum NTFS volume size supported on a GPT disk. It depends on the cluster size that is selected at the time of formatting. NTFS is currently limited to 2^32-1 allocation units. This yields a 256TB volume, using 64k clusters. However, this has only been tested to 16TB, or 17,592,186,040,320 bytes, using 4K cluster size. You can read up on this in Frequently asked questions about the GUID Partitioning Table disk architecture. The table below shows the NTFS limits based on cluster size.

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This was the first time I had the opportunity to test these limits I formatted part of that LUN to a size close to the limit and than formatted the remainder to a second simple volume.

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I still need get a Windows Server 2012 test server hooked up to the SAN. To see if anything has changed there. One thing is for sure, you could put at least 3 64TB VHDX files on a single volume in Windows. Not too shabby Smile. It’s more than enough to put just about any backup software into problems. Be warned, MSFT tested and guarantees performance & behavior up to 64TB in Windows Server 2012, but beyond that you’d better do your own due diligence.

The next thing I’ll do when I have a Windows Server 2012 host hooked up is, is create 64TB VHDX file and see if I can go beyond it before things break. Why, well because I can and I want to take the new SAN and Windows 2012 for a ride to see what boundaries we can push. The SANs are just being set up so now is the time to do some testing.