1. Oracle ZFS Storage Appliance Administration Guide, Release OS8.8.x
  2. Shares and Projects
  3. Project and Share Properties
  4. LUN Local Properties

LUN Local Properties

These properties apply only to LUNs and are not inherited. They cannot be set on projects.

Volume Size

The volume size property is the logical size of the LUN as exported over iSCSI. This property controls the size of the LUN. By default, LUNs reserve enough space to completely fill the volume. Changing the size of a LUN while actively exported to clients may yield undefined results. It may require clients to reconnect and/or cause data corruption on the filesystem on top of the LUN. Check best practices for your particular iSCSI client before attempting this operation.

Thin Provisioned

The thin provisioned property controls whether space is reserved for the volume. By default, a LUN reserves exactly enough space to completely fill the volume. This ensures that clients will not get out-of-space errors at inopportune times. This property allows the volume size to exceed the amount of available space. When set, the LUN will consume only the space that has been written to the LUN. While this allows for thin provisioning of LUNs, most filesystems do not expect to get "out of space" from underlying devices, and if the share runs out of space, it may cause instability and/or data corruption on clients.

When not set, the volume size behaves like a reservation excluding snapshots. It therefore has the same pathologies, including failure to take snapshots if the snapshot could theoretically diverge to the point of exceeding the amount of available space. For more information, see the Reservation property in Managing Filesystem and Project Space.

Thin provisioned LUNs can optionally take advantage of the space reclamation feature that returns free space to the storage pool, as described in Space Reclamation.

The logical block provisioning (LBP) threshold for thin provisioned LUNs is another way to manage space. The LBPthreshold command is available in the RESTful API only, and it sets the LBP threshold for thin provisioned LUNs within a specified storage pool. When set to the default value of 0, the LBP threshold is disabled. To set the threshold, specify the average storage consumption rate. When the threshold value is exceeded, an error message is returned, and you can manage the space accordingly. See also Set LBP Threshold in Oracle ZFS Storage Appliance RESTful API Guide, Release OS8.8.x.

Space Reclamation

The space reclamation property controls whether LUN free space is returned to the storage pool. When set to true, the client operating system issues the SCSI UNMAP command to return unused logically provisioned space after volume data blocks have been deleted by the host operating system. Therefore, this property must be used in conjunction with the thin provisioned property, which logically sets the volume or LUN size, and it allows the size to exceed the amount of available space, which can be considered free space.

Volume Block Size

The volume block size property sets the native block size for LUNs. This can be any power of 2 from 512 bytes to 1 M, and the default is 8 K. This property is static; it is set when the LUN is created and cannot be changed.

Note:

LUNs with a volume block size smaller than 4 K may cause performance degradation.