Storage Spaces Direct (S2D) is a software-defined storage technology that’s included with the Windows Server 2016 / 2019 Datacenter Edition operating system. When run on industrystandard server hardware with commodity storage devices, S2D can provide the shared capacity for an HCI cluster supporting virtual machines on Hyper-V, which is also included in the Windows Server OS. S2D runs in the Windows Server kernel, not as a VM like the software-defined storage technologies that support most other HCI solutions, providing potential performance and cost advantages.
Azure Stack HCI is the name given to hyperconverged products running Windows Server 2019 and marketed by server vendors in partnership with Microsoft, including Dell EMC, HPE, Fujitsu, Lenovo, Axellio, Supermicro and others. HCI solutions using Windows Server 2016, which include essentially the same vendors, are still called the Windows Server Software Defined (WSSD) program.
While Storage Spaces Direct isn’t the name of an HCI product, per se, it does provide most of the differentiation between this and other products in this category. For that reason, S2D is mentioned throughout this Product Brief, sometimes interchangeably with Azure Stack HCI. Azure Stack HCI clusters contain a minimum of two nodes, a maximum of sixteen, with a max capacity of 4PB (raw). All servers must have the same number of drives and Microsoft recommends that server nodes be of the same make and model. Nodes can be configured with either storage or compute functions on each node, enabling the cluster to scale storage and compute resources independently. Microsoft calls this the “converged” mode. S2D can also be set up with both storage and compute functions residing on the same node, called the “hyperconverged” mode.
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