ONTAP 9 Manuals ( CA08871-402 )

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Enable space allocation for SAN

If your FC or iSCSI host supports SCSI thin provisioning, you can enable space allocation. When space allocation is enabled and a volume runs out of space, the LUN in the volume remains online and is set to read-only mode. The host is then notified that the LUN can no longer accept writes. If space allocation is not supported on your host or is not enabled, when a volume runs out of space and cannot automatically grow, ONTAP takes the LUN offline.

Also, when space allocation is enabled, host-side space management identifies blocks of data that have been deleted on the host file system and automatically issues one or more SCSI UNMAP commands to free corresponding blocks on the storage system and allow ONTAP to reclaim space.

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 and later

  • ESXi 5.0 and later

  • Oracle Linux 6.2 UEK kernel and later

  • Red Hat Enterprise Linux 6.2 and later

  • SUSE Linux Enterprise Server 11 and later

  • Solaris 11.1 and later

  • Windows

Space allocation is not supported on NVMe hosts.

About this task

Beginning with ONTAP 9.15.1, space allocation is enabled by default for newly created VMware and Hyper-V LUNs and is disabled for all newly created LUNs not used by VMware and Hyper-V.

When you upgrade your cluster to ONTAP 9.15.1, the space allocation setting for all LUNs created prior to the software upgrade remains the same after the upgrade, regardless of host type. For example, if a LUN was created in ONTAP 9.13.1 for a VMware host with space allocation disabled, space allocation on that LUN remains disabled after upgrading to ONTAP 9.15.1.

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.

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