GLYPH<SM590000> Always cross-check the host LUN ID information with the vdisk_UID of the SAN Volume Controller. Do not assume that the operating system recognizes, creates, and numbers the disk devices in the same sequence or with the same numbers as you created them in the SAN Volume Controller/Storwize. 

GLYPH<SM590000> Ensure that you delete any volume or LUN definition in the server before  you unmap it in IBM Spectrum Virtualize. For example, in AIX, remove the hdisk from the volume group ( reducevg ) and delete the associated hdisk device ( rmdev ). 

GLYPH<SM590000> From version 7.4 onwards, consider enabling volume protection by using chsystem -vdiskprotectionenabled yes -vdiskprotectiontime <value_in_minutes> . Volume protection ensures that some CLI actions (most of those that either explicitly or implicitly remove host-volume mappings or delete volumes) are policed to prevent the removal of mappings to volumes or deletion of volumes that are considered active  (the system has detected I/O activity within the specified time in minutes to the volume from any host). 

Note:  Volume protection cannot be overridden by the use of the -force  flag in the affected CLI commands. Volume protection must be disabled to carry on an activity that is currently blocked. 

GLYPH<SM590000> Ensure that you explicitly remove a volume from any volume-to-host mappings and any copy services relationship to which it belongs before  you delete it. 

Attention:  You must avoid the use of the -force  parameter in rmvdisk . 

If you issue the svctask rmvdisk  command and it still has pending mappings, IBM Spectrum Virtualize prompts you to confirm and is a hint that you might have done something incorrectly. 

GLYPH<SM590000> When you are deallocating volumes, plan for an interval between unmapping them to hosts ( rmvdiskhostmap ) and deleting them ( rmvdisk ). The IBM internal Storage Technical Quality Review Process (STQRP) asks for a minimum of a 48-hour period, and having at least a one business day interval so that you can perform a quick backout if you later realize you still need some data on that volume. 

## 9.3.2 Adding and removing hosts 

When you add and remove a host (or hosts) in IBM Spectrum Virtualize, consider the following guidelines: 

GLYPH<SM590000> Before you map new servers to IBM Spectrum Virtualize, verify that they are all error free. Fix any errors that you find in your server and IBM Spectrum Virtualize before you proceed. In IBM Spectrum Virtualize, pay special attention to anything inactive in the svcinfo lsfabric  command. 

GLYPH<SM590000> Plan for an interval between updating the zoning in each of your redundant SAN fabrics, such as at least 30 minutes. This interval allows for failover to occur and stabilize, and for you to be notified if unexpected errors occur. 

GLYPH<SM590000> After you perform the SAN zoning from one server’s HBA to IBM Spectrum Virtualize, you should list its WWPN by using the svcinfo lshbaportcandidate  command. Use the svcinfo lsfabric  command to certify that it was detected by the IBM Spectrum Virtualize nodes and ports that you expected. When you create the host definition in IBM Spectrum Virtualize ( svctask mkhost ), try to avoid the -force  parameter. If you do not see the host’s WWPNs, it might be necessary to scan fabric from the host. For example, use the cfgmgr command in AIX. 

