VPLEX: VPLEX takes 3x-4x longer to free up space compared to Native SCSI UNMAP on supported arrays

           

   Article Number:     502965                                   Article Version: 3     Article Type:    Break Fix 
   

 


Product:

 

VPLEX Series,VPLEX Local,VPLEX Metro,VPLEX GeoSynchrony,VPLEX GeoSynchrony 5.5 Service Pack 1,VPLEX GeoSynchrony 5.5 Service Pack 1 Patch 1,VPLEX GeoSynchrony 5.5 Service Pack 1 Patch 2,VPLEX GeoSynchrony 5.5 Service Pack 2

 

Issue:

 

 

In the current VPLEX UNMAP SCSI command implementation, UNMAP SCSI command completion latency is expected to be 3x-4x longer than native XtremIO/VNX/Unity/VMAX array implementation of the SCSI UNMAP command. Storage reclamation using UNMAP SCSI commands is a maintenance activity. Users should consider the increased processing time required in order to reclaim storage through VPLEX and plan accordingly.   
   
    Typically, VPLEX average latency in completing individual SCSI UNMAP command is in sub seconds. VPLEX provides the following UNMAP SCSI command statistics:   

         
  •         The number of UNMAP SCSI commands per second seen at the target     
  •      
  •         The average latency in quarters per second of UNMAP SCSI command at the target     
  •    
   
    These statistics work with the following targets:   
         
  •         front-end port     
  •      
  •         front-end director     
  •      
  •         front-end logical unit     
  •      
  •         host initiator port     
  •    
   
    Users must create new monitors to read these statistics. Please refer to the VPLEX documentation for details about creating new VPLEX monitors                                                           

 

 

Cause:

 

 

Current VPLEX UNMAP implementation can only issue maximum 1MB UNMAP in its request to XtremIO storage volume compared to host issuing 4MB UNMAP when XtremIO SV is directly used by the host.  This VPLEX implementation limitation is the main cause for the decreased VPLEX UNMAP performance.  UNMAP is considered as a maintenance activity to free unused blocks at a host-application-convenient time and therefore UNMAP performance was considered as a secondary goal in the VPLEX implementation.                                                            

 

 

Resolution:

 

 

This is an expected behavior. Customers should consider the increased processing time required in order to reclaim storage through VPLEX and plan accordingly.