Thin provisioning using the NAS server filesystem-thin command

Storage Subsystem Administration Guide for Hitachi NAS Platform

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HDP thin provisioning differs from thin provisioning achieved by the NAS server's filesystem-thin command.

  • The filesystem-thin command instructs the server to report an artificially large file system to NFS and SMB clients. It bypasses free-space checks in programs that are not aware that file systems can expand on demand and reports large file system capacities to tenants even when the file systems are newly created and are still small.
  • HDP thin provisioning instructs the block storage to report artificially large capacities for system drives. It enables spans to be expanded in smaller increments without loss of performance, and it widens the storage bottleneck by helping to spread I/O across all available storage media.

The two types of thin provisioning are commonly used together. They both enable Administrators to delay the purchase of new storage until it is actually needed.

To enable thin provisioning using the filesystem-thin command:

  1. Create a small file system.
  2. Confine it (using the filesystem-confine command) to a larger capacity.
  3. Use the filesystem-thin command to enable thin provisioning on that file system.

Now, if applications or NFS and SMB clients ask for the capacity of the file system, they are told that the capacity is the confined amount, even though the actual amount of disk capacity allocated to the file system is less. As data is written to the file system, the file system grows, but only up to the maximum amount to which the file system has been confined, and no further.

Note: A NAS server storage pool can contain a mixture of thinly and thickly provisioned file systems.