Tag Archives: High Availability

Continuous available general purpose file shares & ReFSv3 provide high available backup targets

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Introduction

In our previous two blog posts on Veeam and SMB 3 we’ve seen how and when Veeam Backup & Replication can leverage SMB Multichannel and SMB Direct. See Veeam Backup & Replication leverages SMB Multichannel and Veeam Backup & Replication Preferred Subnet & SMB Multichannel.The benefits of this are more bandwidth, high availability, better throughput and with RDMA low latency and CPU offload. What’s not to like, right? In a world where the compute and networks need keeps rising due to the storage capabilities (flash storage) pushing the limits this is all very welcome.

We have also seen earlier that Veeam B & R 9.5 leverages ReFSv3 in Windows Server 2016. This provides clear and present benefits in regards to space efficiencies and speed with many backup file related operations. Read Veeam Leads the way by leveraging ReFSv3 capabilities

When it comes to ReFSv3 in Windows Server 2016 most of the focus has gone to solutions based around Storage Spaces Direct (S2D). That’s a great solution and it is the poster child use case of these technologies.

But what other options do you have out there to build efficient and effective high available backup targets creatively except for S2D? What if you would like to repurpose existing hardware to build those? Let’s take a look together at how continuous available general purpose file shares & ReFSv3v3 provide high available backup targets

CSV, S2D, ReFSv3 & Archival Data

In Windows Server 2016, traditional shared storage (iSCSI, FC, Shared SAS, Shared RAID) with CSV are not recommend to be used with ReFSv3. Why isn’t exactly clear. The biggest impact you’ll see is the performance difference when not writing to the owner node of the CSV in this use case. Even with a well configured RDMA network that difference is significant. But that doesn’t mean that the performance is bad. It’s just that many of the super-fast meta data operations are relatively and significantly slower when compared each other, not that any of these two are slow.

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Microsoft does state that an S2D with ReFSv3 and SOFS shares can be used for archival data. Storage spaces and ReFSv3 also have the benefit of offering automatic repair of corrupt data from a redundant copy on the fly even when needed. So yes, the best know supported scenario is this one.

Continuous available general purpose file shares and ReFSv3 provide high available backup targets

But what if we need a high available backup target and would love to leverage ReFSv3 with Veeam Backup & Replication 9.5? Well, you can have 95% of your cookie and eat it to. All this without ignoring the cautions offered.

We could set up SOFS shares on a Windows Server 2016 Cluster with ReFSv3 with traditional shared storage. Some storage vendors do state this is supported actually.

That only means you don’t have the auto repair functionality ReFSv3 combined with storage spaces offers. But perhaps you want to avoid the risk of using ReFSv3 with CSV in a non S2D scenario all together. What you could do is forgo ReFSv3 and use NTFS. How well this will work for archival data or backup is something you’ll need to test and find out how well this holds up. There is not much info is out there, only other cautions and warnings that might keep you up at night.

There is another scenario however and that is using Windows Server 2016 failover clustering to set up continuously available general purpose file shares that leverage SMB3 transparent failover.

The good news is that general purpose file shares (no CSV) do work consistently with ReFSv3 because such a share/LUN is only exposed on one cluster node at the time, the owner. By having multiple shares and setting preferred owners we can load balance the workload across all cluster nodes.

Thank to continuous availability for general file shares and SMB 3 transparent failover we can still get a high available backup target this way. The failover is fast enough to make this happen and all we see with Veeam Backup & Replication is a short pause in throughput before it resumes after failover. To put the icing on the cake, you can leverage SMB multichannel SMB Direct for both backup and restores.

I would take a sizeable whitepaper to walk through the setup so instead I’ll show you a a quick video of a POC we did in the lab here https://vimeo.com/212886392.

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If you want to learn more come to the community & other conferences I’m speaking at and will be around for Ask The Experts time opportunities. I’ll be at the German Hyper-V community meet up, The Cloud & Datacenter Conference in Germany 2017, Dell EMC World 2017 and last but not least VeeamON 2017 (see  May 2017 will be a travelling month). 

Conclusion

What do you lose?

Potentially there is one big loss in regards to the capabilities of ReFSv3 with this solution when you are not using storage spaces. This is that you lose the capability to automatic repair of corrupt data. The ability of ReFSv3 to do so is tied into the redundant copies of Storage Spaces (parity/mirror).

What do you get?

That’s fine, the strength of this design is that you get the speed and space efficiencies of ReFSv3and high available backup targets in way more scenarios than “just” S2D. After all, not everyone is in a position to choose their storage fabric for backup targets green field or at will. But they might be able to leverage existing storage and opt to use SMB 3 for their data transport.

So even if you can’t have it all, you can still build very good solutions. It offers ReFSv3 benefits and high availability for your backup target via transparent failover with SMB transparent failover on continuous available general purpose file shares. This also only requires Windows Server 2016 Standard Edition, which is a cost saving. You get to leverage SMB Multichannel and SMB Direct. All this while not ignoring the cautions of using ReFSv3 in certain scenarios.

On top of that, if you use NTFS with this approach it will also work for Windows Server 2012 (R2) as the OS for the backup target cluster hosts.

Disclaimer

I do not work for or at Microsoft, nor am I perfect or infallible just because I’m an MVP. You’ll have to do your own testing and validation. From our testing and without ReFSv3 bugs ruining the show, to me this is a very valid and cost effective approach.

High Availability has a price

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We’ll go back to basics today. Some times the obvious, no matter how evident it is to us technologists, is challenged. Recently we got the remark that we were wasting CPU cycles by assigning to many vCPU to certain virtual machines on our Hyper-V cluster. So we had to explain that high availability has a price. On top of that we had to explain that things are not as wasteful as they seem in a virtual environment.

The case

Here’s one of the “offending” virtual machines. They assumed that we are wasting at least 50% of 12 CPUs.

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This is one node in a dual node  load balancing (active-active) and highly available solution. This provides for zero down time during scheduled maintenance and very little downtime during system failures.

And here’s the second node (yes the 1st node has been down for scheduled maintenance more recently that node 2).

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In a 2 node HA solution you need to make sure that one node can handle the entire workload. This is the absolute border line of an N+1 solution.  This means you can lose 1 node. N determines the number of nodes needed to guarantee an agreed upon service level and the number defines how many nodes failures can be tolerated before affecting the service.

In the above example there’s a need to have the CPU resources on each node to run the entire workload on one node without having an effect on the service. Therefore, when both nodes are up this might seem like a waste to the uninitiated. It is however a required to achieve the high availability goal. A constant CPU usage over 75 % will lead to a reduction in service quality in this case and even compromise the usability of the that service.

I did not even dive into the dangers of designing purely based on averages during this “explanation”. That was one step to much for the level of the discussion.

It’s also important to note that Hyper-V CPU scheduling is highly intelligent and is far less susceptible to the waste of CPU cycles via over provisioning of vCPU than some other solutions are or used to be. Knowing the capabilities and inner working of the technology used is also important in all this. More nodes generally also make “over provisioning” less of an issue. When you have 10 nodes and you lose 1, you only have lost 10% of the capabilities, not 33% like in a 3 node cluster.

Ideally you have 3 node so that even during an issue with one node you still maintain redundancy. However if you want acceptable services during a 2 node failure you’ll need to go to N+2, meaning that you need 2 nodes to provide the services and handle losing 2 nodes gracefully. In that case you’ll need 4 node and so on.  The larger the node count  the wiser it is to go to a N+2 model and ideally you’ll provide separate failure domains over which the nodes are distributed. An example of this is having a redundant geo-load balanced web farm of 32 virtual machine nodes spread over 2 locations and running on separate hardware failover clusters in each location. As you can see the higher the stakes and demands the faster the cost and potential complexity rises. You can offload some of the complexity by leveraging a public cloud like Azure, but the costs will still be there. There is no such thing as a free lunch, some are quite easy and affordable for what you get.

Conclusion

High Availability has a price. I did mention that already, right? To be able to keep your services running at a level that is both workable and acceptable to your customers and stake holders you will need to over provision to a degree. There is no magic here. When your solutions are being scrutinized by people with no real background, experience and context in high availability you might need to explain this.

Exchange 2010 SP1 Public Folder High Availability Returns with Roll Up 2

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Al lot of people were cheering in the inter active session on Exchange 2010 SP1 High Availability with Scott Schnoll and Ross Smith of the Exchange Team. They announced (between goofing around) that the alternate server that provides failover to the clients (so they can select another public folder database to connect to) for public folders and that is sadly missing from Exchange 2010 would return with Exchange 2010 SP 1 Roll Up 2. This feature is needed by Outlook to automatically connect to an alternate public folder and it’s return means that high availability will finally be achievable for public folders in Exchange 2010 SP1. That’s great news and frankly an “oversight” that shouldn’t have happened even in Exchange 2010 RTM. The issue is described in knowledge base article “You cannot open a public folder item when the default public folder database for the mailbox database is unavailable in an Exchange Server 2010 environment” which you can find here  http://support.microsoft.com/kb/2409597.

In previous versions of exchange you made public folders highly available to Outlook clients by having replica’s. The Outlook clients could access an replica on another server if the default public folders as defined in the client settings of the database was not available. Clustering in Exchange 2010 does nothing for public folders. In Exchange 2010 the Outlook clients connect directly to the mailbox server in order to get to a public folder so they do not leverage the CAS or CAS array. Also the DAG does not support public folders and as clustering happens at the database level on DAG members and no longer at the server level we no longer get any high availability for the clients with clustering in Exchange 2010. Sure, if you have multiple replica’s the data is highly available but the access to another replica/database/server for public folder doesn’t happen automatically in Outlook when you’re running Exchange 2010. To make that happen you need an alternate server to be offered to the client for selection But as this feature is missing in Exchange 2010 up until SP1 Roll Up 1 in reality until now you need to keep using Exchange 2003/2007 to have public folder high availability.  Exchange 2010 SP1 Roll Up 2 will change that. I call that good news.