What are the recommendations for the host stacks supporting SCSI UNMAP (TRIM) commands?
Applies to
Clustered Data ONTAP 8
Answer
The UNMAP
command is a SCSI command standardized within the T10 SCSI command set used to reclaim space from blocks that have been deleted by the host OS, an application, or a virtual machine. Thin provisioning technology broadly adopted in the current computer industry uses the UNMAP
command to achieve improved storage utilization, flexible capacity planning, and non-stop storage provisioning service. The UNMAP
command can be used as an inline or as an offline operation.
Support for the UNMAP
command has been added for Data ONTAP 8.1.3 and later.
Host stacks support the UNMAP
command to different degrees.
The following is a summary of general recommendations for various host stacks:
Windows:
NTFS in Server 2012 and later will support the UNMAP
command. To enable the inline UNMAP
command, use HUK 6.0.2 or ONTAPDSM 4.0 or later
VMware:
ESX 5.0U1 disables the UNMAP
command. It is recommended to use vmkfstools to reclaim space.
For more information on guidelines, see VMware KB 2007427
For more information on how to reclaim space see VMware KB 2014849
Linux:
RHEL uses discard operations to reclaim space through the UNMAP
command. It supports both online discard (fine-grained discard using the –o discard mount
option) and offline discard (batch discard using the fstrim utility).
Red Hat recommends using batch discard operations unless the system's workload is such that the batch discard is not feasible, or online discard operations are necessary to maintain performance. For more information, see the RHEL6 Storage Admin Guide
Solaris:
Solaris does not support SCSI unmap for file system UFS. Since Solaris 11.1 (Oct. 2012) ZFS supports SCSI unmap. This has been backported to Solaris 10 with patch 150400-16.
AIX and HPUX:
These operating systems do not support the UNMAP
command.
Symantec:
Symantec does not support the inline UNMAP
command for Solaris/Linux and AIX. For more information on using the UNMAP
command, see the section on Thin Reclamation in the Symantec Storage Foundation Administrator's Guide.
Additional Information
additionalInformation_text