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Enable space allocation for SCSI thinly provisioned LUNs

Contributors netapp-aherbin
PDFs

If your host supports SCSI thin provisioning, you can enable space allocation for SCSI thinly provisioned LUNs in ONTAP. When space allocation is enabled, ONTAP notifies the host when the volume has run out of space and the LUN in the volume cannot accept writes. ONTAP also automatically reclaims space when your host deletes data.

On hosts that do not support SCSI thin provisioning, when the volume containing LUN runs out of space and cannot automatically grow, ONTAP takes the LUN offline. On hosts that support SCSI thin provisioning, ONTAP does not take the LUN offline when it runs out of space. The LUN remains online in read-only mode and the host is notified that the LUN can no longer accept writes.

Also, when data is deleted on a host that supports SCSI thin provisioning, host-side space management identifies the blocks of deleted data on the host file system and automatically issues one or more SCSI UNMAP commands to free corresponding blocks on the storage system.

Before you begin

To enable space allocation, SCSI thin provisioning must be supported by your host. SCSI thin provisioning uses logical block provisioning as defined in the SCSI SBC-3 standard. Only hosts that support this standard can use SCSI thin provisioning in ONTAP.

The following hosts currently support SCSI thin provisioning when you enable space allocation:

  • Citrix XenServer 6.5 & later

  • ESXi 5.0 & later

  • Oracle Linux 6.2 UEK kernel or later

  • RHEL 6.2 & later

  • SLES11 & later

  • Solaris 11.1 & later

  • Windows

About this task

By default, space allocation is disabled for all LUNs. You must take the LUN offline to enable space allocation; then you must perform discovery on the host before the host will recognize that space allocation has been enabled.

Steps

  1. Take the LUN offline.

    lun modify -vserver vserver_name -volume volume_name -lun lun_name -state offline

  2. Enable space allocation:

    lun modify -vserver _vserver_name_ -volume _volume_name_ -lun _lun_name_ -space-allocation enabled

  3. Verify that space allocation is enabled:

    lun show -vserver _vserver_name_ -volume _volume_name_ -lun _lun_name_ -fields space-allocation

  4. Bring the LUN online:

    lun modify -vserver _vserver_name_ -volume _volume_name_ -lun _lun_name_ -state online

  5. On the host, rescan all disks to ensure that the change to the -space-allocation option is correctly discovered.