Data center convergence and the role of storage
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At the heart of any converged vs. hyper-converged infrastructure debate is the storage layer that contains the...
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physical components necessary to support data operations.
To a great degree, storage drives the system architecture, regardless of the implementation type. One way to think of a converged or hyper-converged infrastructure is as a data storage platform that integrates compute, virtualization and, sometimes, networking technologies with the storage mechanisms.
However, converged infrastructure (CI) and hyper-converged infrastructure (HCI) support storage capabilities in different ways, and that difference represents one of the fundamental ways these systems diverge. CI is primarily a hardware-based system, while HCI is a software-based one, and that makes all the difference in providing integrated storage.
Converged infrastructure storage
To understand how storage works in a converged vs. hyper-converged infrastructure system, it helps to have a big picture of the entire infrastructure to see where storage fits.
A converged system blends compute, network, storage and virtualization technologies into a single integrated infrastructure bundle, optimized for specific workload types. While CI is purchased as one package, the storage, compute and network are separate pieces.
CI components are often delivered as single- or multirack unified systems that include all the resources necessary to deliver a complete and integrated data platform. You can scale the system by adding individual components, or blocks, to the racks. However, the components themselves remain discrete resources that can be used for other purposes.
A converged platform is a highly optimized, engineered system that provides a single resource pool for delivering services, which helps to simplify implementation and management, while better utilizing components when compared to a nonconverged system.
CI storage is directly attached to the other components within the rack structure. Although the exact architecture varies from one product to the next, the end result is a system whose storage arrays are integrated with the server and network resources in a SAN.
Most converged platforms support a mix of HDDs and solid-state drives (SSDs). As with storage arrays in general, these are usually hybrid or all-flash models today. For example, the Dell EMC VxBlock and Vblock System 740 products let you choose from several VMAX hard disk arrays and several VMAX all-flash arrays when putting together a system. Each option comes with one or more storage engines for managing the physical drives.
Converged systems often include switches in the network layer to support SAN connectivity with the storage devices. Each switch serves as an interface between the compute layer and the storage layer. For example, VxBlock and Vblock use Cisco MDS multilayer fabric switches to provide SAN switching and routing between the two layers.
Hyper-converged infrastructure storage
A hyper-converged system takes convergence to a new level, with a software-centric approach to integrating the compute, storage and, sometimes, network resources into a single appliance.
Each appliance is a self-contained node that you can scale by adding additional nodes, which are tied together into a cluster with a single storage pool. You cannot use the individual components for other purposes because of a hyper-converged infrastructure's highly integrated, software-based nature of a hyper-converged infrastructure. Each node is essentially a server, with its own direct-attached storage, but grouped together with other nodes through its software-driven architecture.
As with a converged appliance, a hyper-converged appliance uses virtualization technologies to deliver a single resource pool. However, there is one important difference in converged vs. hyper-converged infrastructure in this area: Despite virtualization, converged infrastructure still remains a hardware-based approach, and it brings with it the limitations that come with interfacing directly with hardware components.
Hyper-converged infrastructure breaks free from these limitations by integrating a software layer that abstracts the physical hardware, including the storage layer. This streamlines operations and improves resource utilization, and can also provide additional services, such as disaster recovery, deduplication and replication.
The direct-attached storage that comes with a hyper-converged appliance is usually made up of HDD and SSD components, although all-flash CI versions are also gaining in popularity. With HCI, the storage is aggregated across all the nodes to deliver a software-defined data center, without needing physical SAN or NAS components.
The key to all this is the software that abstracts the underlying hardware and aggregates the storage from different nodes into a single resource pool. Each node runs a storage controller service that works in orchestration with the controllers on other nodes to provide a unified storage system.
For example, the Dell EMC VxRail appliance uses VMware's Virtual SAN (vSAN) to provide the necessary interface. The vSAN software, which is embedded in the ESXi kernel layer, aggregates the locally attached HDD and SSD components to create a virtual pool of distributed shared storage, resulting in a fully integrated, software-defined storage system.
Hewlett Packard Enterprise takes a similar approach in its HPE Reference Architecture for VMware Horizon on HPE Hyper Converged 380. The appliance uses the HPE StoreVirtual Virtual Storage Appliance software to consolidate the nodes into a single virtual storage pool.
Nutanix supports VMware hypervisors, but uses its own Prism management software for data services, instead of vSAN. Nutanix also has Acropolis Hypervisor as an alternative for vSAN, or for customers who want multi-hypervisor support. The underlying hardware for Nutanix appliances consists of x86 servers; in some cases, the same Dell EMC PowerEdge servers used in VxRail appliances.
Some vendors sell software as a stand-alone product, allowing organizations to assemble an HCI using their components of choice. For example, Maxta offers Maxta Storage Platform, a software-defined storage product that maps virtual machines to storage resources to create a virtual storage pool.
Converged vs. hyper-converged infrastructure approaches
Both converged and hyper-converged infrastructure offer data storage options that simplify implementation and use resources more efficiently than traditional systems. Each system also integrates storage with other components, using virtualization to help deliver a single resource pool made up of HDDs and SSDs.
However, CI and HCI take different approaches to how they deliver that storage. Despite their use of virtualization technologies, CI remains primarily a hardware-based option, while HCI is a software-based approach. Of course, there are other features that set them apart, but the software aspect alone is enough to clearly distinguish one from the other.
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