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Figure 2-60:
The Storage Spaces Direct stack 
The updated stack includes the following, starting from the bottom: 

Hardware The storage system consists of a minimum of four storage nodes with local storage. 
Each storage node can have internal drives or drives in an external SAS-connected JBOD 
enclosure. The drive devices can be SATA disks or SAS disks. 

Software Storage Bus The Software Storage Bus spans all of the storage nodes and brings 
together the local storage in each node, so all drives are visible to the Storage Spaces layer above. 

Storage Spaces Storage Spaces provides storage pools and virtual drives. The storage pool can 
span all of the local storage across the nodes. The virtual drives provide resiliency to drive or node 
failures because data copies are stored on different storage nodes. 

Resilient File System (ReFS) ReFS provides the file system in which the Hyper-V VM files are 
stored. ReFS is a premier file system in Windows Server 2016 for virtualized deployments and 
includes optimizations for Storage Spaces such as error detection and automatic correction. In 
addition, ReFS provides accelerations for VHD(X) operations such as fixed VHD(X) creation, 
dynamic VHD(X) growth, and VHD(X) merge. CSVFS layers above ReFS bring all the mounted 
volumes into a single namespace. 

SOFS This is the top layer of the storage stack that provides remote access to the storage 
system by using the SMB 3.0 access protocol. 
Improved scalability 
You can deploy Storage Spaces Direct using storage nodes with either local storage or nonshared 
JBODs. In previous versions of Windows Server, scaling out Storage Spaces solutions required a 
concurrent increase in the scale of the SAS fabric that joined the storage nodes to the shared SAS 
JBODs. In contrast, with Storage Spaces Direct, you can set up a model that removes the complexities 
of the SAS fabric, making scale-out as simple as adding a new storage node, either with internal 
storage or attached to a nonshared JBOD. Scaling out by adding storage nodes provides more 
flexibility in storage planning because storage expansion is no longer bound by the number of drive 
slots in a shared SAS JBOD. 

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CHAPTER 2 | Software-defined datacenter 
To support this model of just-in-time scale-out, Storage Spaces Direct improves scalability compared 
to previous versions of Windows Server because you can now manage more drive devices in a single 
storage pool. Increasing the number of drive devices in a single pool reduces the number of storage 
pools that you must create, simplifying management of the storage solution.