Chapter 7. Volumes 255
To address this issue, file systems added support for SCSI unmap command, which can be 
issued after file deletion, and informs the storage system that physical blocks that are used by 
the removed file should be marked as no longer in use and can be freed up. Modern 
operating systems issue SCSI unmap commands only to storage that advertises support for 
this feature. 
V8.1.0 and later releases support the SCSI unmap command on Spectrum Virtualize systems 
(including SAN Volume Controller, Storwize V5000, Storwize V7000, and FlashSystem 
V9000). This enables hosts to notify the storage controller of capacity that is no longer 
required and may be reused or de-allocated, which might improve capacity savings. 
Consider the following points:
/SM590000V8.1.2 can also reclaim capacity in data reduction pools when a host issues SCSI unmap 
commands.
/SM590000By default, V8.2.1 does not advertise to hosts support for SCSI unmap. 
Before enabling SCSI unmap, see this IBM Support web page.
Analyze your storage stack to optimally balance advantages and costs of data reclamation.
7.1.12  Virtual volumes
IBM Spectrum Virtualize V7.6 introduced support for virtual volumes. These volumes enable 
support for VMware vSphere Virtual Volumes (VVols), which allow VMware vCenter to 
manage system objects, such as volumes and pools. The IBM Spectrum Virtualize system 
administrators can create volume objects of this class, and assign ownership to VMware 
administrators to simplify management.
For more information about configuring VVol with IBM Spectrum Virtualize, see Configuring 
VMware Virtual Volumes for Systems Powered by IBM Spectrum Virtualize, SG24-8328.
7.1.13  Volumes in multi-site topologies
IBM Spectrum Virtualize system can be set up in a multi-site configuration, which makes the 
system aware of which system components (I/O groups, nodes, and back-end storage) are at 
which site. For the purpose of defining the storage topology, a site is defined as an 
independent failure domain, which means that if one site fails, the other site can continue to 
operate without disruption. 
The sites can be in the same data center room or across rooms in the data center, in buildings 
on the same campus, or buildings in different cities, depending on the type and scale of a 
failure the solution must survive. 
The following topologies are available for IBM Spectrum Virtualize that is running on Storwize 
V7000:
/SM590000Standard topology, which is intended for single-site configurations that does not allow site 
definition and assumes all components of the solution to be at a single site. Global Mirror 
or Metro Mirror can be used to maintain a copy of a volume on a different system at a 
remote site, which can be used for disaster recovery. 
Note: For volumes that are outside data reduction pools, the complete stack from the 
operating system down to back-end storage controller must support unmap to enable the 
capacity reclamation. SCSI unmap is passed only to specific back-end storage controllers.