Chink in NetApp MetroCluster?

Ok, let me clear the air about the word “Chink” (before I get into trouble), which is not racially offensive unlike the news about ESPN having to fire 2 of their employees for using the word “Chink” on Jeremy Lin.  According to my dictionary (Collins COBUILD), chink is a very narrow crack or opening on a surface and I don’t really know the derogatory meaning of “chink” other than the one in my dictionary.

I have been doing a spot of work for a friend who has just recently proposed NetApp MetroCluster. When I was at NetApp many years ago, I did not have a chance to get to know more about the solution, but I do know of its capability. After 6 years away, coming back to do a bit of NetApp was fun for me, because I was always very comfortable with the NetApp technology. But NetApp MetroCluster, and in this opportunity, NetApp Fabric MetroCluster presented me an opportunity to get closer to the technology.

I have no doubt in my mind, this is one of the highest available storage solutions in the market, and NetApp is not modest about beating its own drums. It touts “No SPOF (Single Point of Failure“, and rightly so, because it has put in all the right plugs for all the points that can fail.

NetApp Fabric MetroCluster is a continuous availability solution that stretches over 100km. It is basically a NetApp Cluster with mirrored storage but with half of  its infrastructure mirror being linked very far apart, over Fibre Channel components and dark fiber. Here’s a diagram of how NetApp Fabric Metrocluster works for a VMware FT (Fault Tolerant) environment.

There’s a lot of simplicity in the design, because when I started explaining it to the prospect, I was amazed how easy it was to articulate about it, without all the fancy technical jargons or fuzz. I just said … “imagine a typical cluster, with an interconnect heartbeat, and the storage are mirrored. Then imagine the 2 halves are being pulled very far apart … That’s NetApp Fabric MetroCluster”. It was simply blissful.

But then there were a lot of FUDs (fear, uncertainty, doubt) thrown in by the competitor, feeding the prospect with plenty of ammunition. Yes, I agree with some of the limitations, such as no SATA support for now. But then again, there is no perfect storage solution. In fact, Chris Mellor of The Register wrote about God’s box, the perfect storage, but to get to that level, be prepared to spend lots and lots of money! Furthermore, once you fix one limitation or bottleneck in one part of the storage, it introduces a few more challenges here and there. It’s never ending!

Side note: The conversation triggered the team to check with NetApp for SATA support in Fabric MetroCluster. Yes, it is already supported in ONTAP 8.1 and the present version is 8.1RC3. Yes, SATA support will be here soon. 

More FUDs as we went along and when I was doing my research, some HP storage guys on the web were hitting at NetApp MetroCluster. Poor HP! If you do a search of NetApp MetroCluster, I am sure you will come across these 2 HP blogs in 2010, deriding the MetroCluster solution. Check out this and the followup on the first blog. What these guys chose to do was to break the MetroCluster apart into 2 single controllers after a network failure, and attack it from that level.

Yes, when you break up the halves, it is basically a NetApp system with several single point of failure (SPOF). But then again, who isn’t? Almost every vendor’s storage will have some SPOFs when you break the mirror.

Well, I can tell you is, the weakness of NetApp MetroCluster is, it’s not continuous data protection (CDP). Once your applications have written garbage on one volume, the garbage is reflected on the mirrored volume. You can’t roll back and you live with the data corruption. That is why storage vendors, including NetApp, offer snapshots – point-in-time copies where you can roll back to the point before the data corruption occurred. That is why CDP gives the complete granularity of recovery in every write I/O and that’s something NetApp does not have. That’s NetApp’s MetroCluster weakness.

But CDP is aimed towards data recovery, NOT data availability. It is focused on customers’ whose requirements are ability to get the data back to some usable state or form after the event of a disaster (big or small), while the MetroCluster solution is focused on having the data available all the time. They are 2 different set of requirements. So, it depends on what the customer’s requirement is.

Then again, come to think of it, NetApp has no CDP technology of their own … isn’t it?

About cfheoh

I am a technology blogger with 20+ years of IT experience. I write heavily on technologies related to storage networking and data management because that is my area of interest and expertise. I introduce technologies with the objectives to get readers to *know the facts*, and use that knowledge to cut through the marketing hypes, FUD (fear, uncertainty and doubt) and other fancy stuff. Only then, there will be progress. I am involved in SNIA (Storage Networking Industry Association) and as of October 2013, I have been appointed as SNIA South Asia & SNIA Malaysia non-voting representation to SNIA Technical Council. I was previously the Chairman of SNIA Malaysia until Dec 2012. I have recently joined Hitachi Data Systems as an Industry Manager for Oil & Gas in Asia Pacific. The position does not require me to be super-technical (which is what I love) but it helps develop another facet of my career, which is building communities and partnership. I think this is crucial and more wholesome than just being technical alone. Given my present position, I am not obligated to write about HDS and its technology, but I am indeed subjected to Social Media Guidelines of the company. Therefore, I would like to make a disclaimer that what I write is my personal opinion, and mine alone. Therefore, I am responsible for what I say and write and this statement indemnify my employer from any damages.
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