Yo everyone…This is going to be a short blog post in this series. I am just covering Networking and Storage QoS as it pertains to S2D. There are the technologies the bind S2D together. Storage QoS
S2D is using the Storage (QoS) Quality of Service that ships with Windows Server 2016 which provides standard min/max IOPS and bandwidth control. QoS policy can be applied at the VHD, VM, Groups of VMs, or Tenant Level. Benefits include:
Mitigate noisy neighbor issues. By default, Storage QoS ensures that a single virtual machine cannot consume all storage resources and starve other virtual machines of storage bandwidth.
Monitor end to end storage performance. As soon as virtual machines stored on a Scale-Out File Server are started, their performance is monitored. Performance details of all running virtual machines and the configuration of the Scale-Out File Server cluster can be viewed from a single location
Manage Storage I/O per workload business needs Storage QoS policies define performance minimums and maximums for virtual machines and ensures that they are met. This provides consistent performance to virtual machines, even in dense and overprovisioned environments. If policies cannot be met, alerts are available to track when VMs are out of policy or have invalid policies assigned.
What’s New in Networking with S2D? In Windows Server 2016, they added Remote Direct Memory Access (RDMA) support to the Hyper-V virtual switch. For those that don’t know what RMDA is it technology that allows direct memory access from one computer to another, bypassing TCP layer, CPU , OS layer and driver layer. Allowing for low latency and high-throughput connections. This is done with hardware transport offloads on network adapters that support RDMA. Back to Hyper-V virtual switch support for RDMA. This allows you to configure regular or RDMA enabled vNICs on top of a pair of RDMA capable physical NICs. They also added embedded NIC teaming or Switch Embedded Teaming (SET). SET is where NIC teaming and the Hyper-V switch is a single entity and can now be used in conjunction with RDMA NICs, wherein Windows 2012 Server you needed to have separate NIC teams for RDMA and Hyper-V Switch. The images below illustrates the architecture changes between Windows Server 2012 R2 and Windows Server 2016. Next up…Management and Operations…
Fault Tolerance…What does it mean? Let me break it down simply. Pictured above is just a bad design, not fault tolerance. This is not really what fault tolerance means. Having two or more of something is one factor, but how it’s implanted is just as important. Fault Tolerance incorporates two very important principles, High availability and Redundancy. Now if we had a few toilets side by side and kept only 1 open and the other 2 on standby. Also, if it could move the user automatically to another toilet during a failure, then it technically it would be fault tolerant. Anyways, let’s move on from toilets to the real world. 🙂 Simply, Fault Tolerance is the ability to continue non-stop when a hardware failure occurs. A fault-tolerant system is designed from the ground up for reliability by building multiples of all critical components, such as CPUs, memories, disks and power supplies into the same computer. In the event one component fails, another takes over without skipping a beat. Many systems are designed to recover from a failure by detecting the failed component and switching to another computer system. These systems, although sometimes called fault tolerant, are more widely known as “high availability” systems, requiring that the software re-submits the job when the second system is available. True fault tolerant systems with redundant hardware are the most costly because the additional components add to the overall system cost. However, fault tolerant systems provide the same processing capacity after a failure as before, whereas high availability systems often provide reduced capacity. Ok, let move on to fault tolerance in S2D. Fault Tolerance in S2D
Storage Space Direct (S2D) uses 3-way mirroring and will spread those mirrors across 3 different servers in the cluster. S2D supports full chassis and rack awareness and gives you the option to distribute data copies across these fault domains. For disk failures, S2D also uses a self-healing approach… in basic terms, S2D offlines the disk and rebuilds the data copy on another node in the cluster. Replacing a drive adds capacity back into the system. This is important note as not all HCI vendors support self-healing, For example, on VSAN and some other vendors, disk failures take out entire vDisks. Multisite Replication
S2D uses Storage Replica (that ships with Windows Server 2016) for synchronous or async replication. They support both stretched clusters and cluster to cluster DR. Storage Replica is part of Windows Server can be used for other data replication needs outside of S2D. Ok…Next up, Storage QOS and Networking..
Here’s where we dive in and get dirty…but I promise by the end of my series, you will smiling like my friend here. I am planning a surprise with special guest bloggers. Stayed Tuned. Now one to the show…..
The NEW ReFS File System, Multi-Tier Volumes and Erasure Coding
Like S2D, the ReFS file system actually isn’t new either, they have been working on it for several releases now also. In Windows Server 2016, it finally drops the tech preview label and is now ready for production. And there is a lot of benefits… like volume creation doesn’t have to zero out the volume for 10 minutes like NTFS. It’s just a metadata operation that is effectively instantaneous now, I’m just going to focus on the couple of benefits that ReFS has for S2D. For those not familiar Erasure coding (EC) and to prepare you for the next part, EC is a method of data protection in which data is broken into fragments, expanded and encoded with redundant data pieces and stored across a set of different locations. The original goal of EC was to enable data that becomes corrupted at some point in the storage process to be reconstructed by using information about the data that’s stored elsewhere. Erasure codes are great, because of their ability to reduce the time and overhead required to reconstruct data. The drawback of erasure coding is that it can be more CPU-intensive, and that can translate into increased latency. Now all that being said, classic erasure codes were designed and optimized more for communication, not for storage. Naively applying classic erasure codes in storage is okay, but is missing enormous efficiencies. Microsoft has developed their own erasure codes optimized for storage called Local Reconstruction Codes (LRC). I will cover this brieifly further down in the post. Now back on to S2D…For data protection, S2D uses either 3-way mirroring or distributed parity with EC. Mirroring gives you great write performance, but only 33% data efficiency. EC gives you good data efficiency, but random write performance isn’t great for hot data. ReFS supports the ability to combine different disk tiers using different parity schemes in the same vDisk. This allows S2D to do real-time data tiering by writing new data to the mirror tier and then automatically rotating cold data out to the parity tier and applying the erasure code on data rotation. It is important to note that ReFS does not currently support Deduplication. There was a question on this in every session and MSFT says that this is all the ReFS is currently focused on. So we’ll expect to see it land in ReFSv3. For now, customers can get dedupe with S2D by using NTFS. 🙁 Note if you only have two types of storage then the highest performing is used for the cache while the other type will be divided between performance and capacity with the different resiliency option (mirror vs parity) providing the performance/capacity difference between the tiers. If you only have one type of storage then the cache is disabled and the disks divided between performance and capacity like the previously mentioned case. For non-Storage Spaces Direct only two tiers, of storage are supported like Windows Server 2012 R2, i.e. SSD and HDD, there is no cache. If you had NVMe storage that could be the “hot” tier while the rest of storage (SSD, HDD) could be the “cold” tier (you name the tiers whatever you want) but you cannot use three tiers. During Ignite 2016, Microsoft took many shots at VMware. Microsoft said that there’s a right way and a wrong way to do erasure coding. “When you do it the wrong way, performance sucks and you have to limit it to all-flash configurations.” Microsoft research is using a new technique called “Local Reconstruction Codes”. It uses smaller groups within the vDisk that allows them to recover from failures much faster by not having to reconstruct data from across the entire pool. This combined with multi-tier volumes gives S2D good performance, even on hybrid systems. Sounds like a technology that I seen before. Hmmm..I wonder where……. 😉 Ok, that’s all for now. next up, Fault Tolerance and Multisite Replication with S2D….