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Dell EMC Unity™ Family Configuring NFS File Sharing

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Unisphere storage provisioning

Storage provisioning is the process of allocating available drive capacity to meet the capacity, performance, and availability requirements of hosts and applications. When you provision storage with Unisphere, you create storage resources to which hosts and applications can connect in order to access storage.

When you provision a storage resource in Unisphere, the system uses thin provisioning by default. This type of provisioning can improve storage efficiency while reducing the time and effort required for monitoring and rebalancing existing pool resources. Organizations can purchase less storage capacity up front, and increase available drive capacity (by adding drives) on an on-demand basis, and according to actual storage usage, instead of basing drive requirements in the requests or predictions of connected hosts. Thin provisioning allows multiple storage resources to subscribe to common storage capacity within a pool, while the system allocates only a portion of the physical capacity requested by each storage resource. The remaining storage is available for other storage resources to use.

NOTE All storage resources require some amount of metadata from the pools where the storage resources were provisioned.

Thick and thin provisioning

The following table describes the differences between thick and thin provisioning:

Table 1. Differences between thick and thin provisioning
Provisioning type Description
Thick provisioning The amount of storage requested for a storage resource is exclusively allocated for it. This storage is reserved, and the unused portion cannot be used or distributed among other storage resources associated with the same pool.
Thin provisioning The amount of storage requested for a storage resource is not immediately allocated for it. Instead, the system allocates an initial quantity of storage to the storage resource. When the amount of storage consumed within the storage resource approaches the limit of the current allocation, the system allocates additional storage to the storage resource from the pool.

Thin provisioning is required for data reduction.

Figure 1. Difference between thick and thin provisioning

An image that highlights the difference between standard provisioning and thin provisioning.

Creating a thin storage resource

When you create a thin storage resource, you specify a target size for the resource. The size represents the maximum capacity to which the storage resource can grow without being increased by an administrator. The system reserves only a portion of the requested size, called the initial allocation. The requested size of the storage resource represents a subscribed quantity. Additional storage is allocated on-demand.

When a host or application uses approximately 75% of its initial allocation, an additional incremental quantity of storage is automatically allocated to the storage resource. The incremental allocation process continues until the quantity of storage allocated for the storage resource reaches the limit determined by its target size.

NOTE A storage resource may appear full when data copied or written to the storage resource is greater than the space available at that time. When this occurs, the system begins to automatically extend the storage space and accommodate the write operation. As long as there is enough extension space available, this operation will complete successfully.

Pool subscription levels

Because storage resources can subscribe to more storage than is actually available to them, pools can be over-provisioned to support more storage capacity than they actually possess. The system automatically generates notification messages when total pool usage reaches 85% of the pool's physical capacity. (You can customize this threshold.)

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