In this case, check the following areas from an IBM Spectrum Virtualize perspective: From the host perspective, you can experience various situations that range from  performance degradation to inaccessible disks. To diagnose any host-related issue, you can  start checking the hosts configuration on IBM Spectrum Virtualize side. The  Hosts  panel in  the GUI or the following CLI commands should be used to start a verification in any possible  hosts related issue: Check the host’s status. If status is online, it means the host ports are online in both nodes  of an I/O group. If status is offline, it means the host ports are offline in both nodes of an  I/O group. If status is inactive, it means that the host has volumes mapped to it, but all of  its ports have no SCSI commands in the last 5 minutes. And, if status is degraded, it  means at least one of the host ports but not all of them is not online in at least one node of  an I/O group. Example 10-1 shows the  lshost  command output. It shows more details about a specific host, and it is used if you need to identify which host  port is not online in IBM Spectrum Virtualize node or IBM Storwize V7000 controller.  Example 10-2 shows the  lshost <host_id_or_name>  command output. GLYPH<SM590000> The attached hosts. For more information, see 10.3.1, “Host problems” on page 438. GLYPH<SM590000> The SAN. For more information, see 10.3.2, “SAN events” on page 439. GLYPH<SM590000> The attached storage subsystem. For more information, see 10.3.3, “Storage subsystem  issues” on page 440. GLYPH<SM590000> The local FC port masking. For more information, see Chapter 6.1.5, “Port masking” on  page 283. GLYPH<SM590000> lshost GLYPH<SM590000> lshost <host_id_or_name> 438  IBM System Storage SAN Volume Controller, IBM Storwize V7000, and IBM FlashSystem 7200 Best  10.3.1 Host problems Example 10-1 The lshost command Example 10-2 The lshost <host_id_or_name> command IBM_2145:ITSO_DH8_B:superuser> lshost id name port_count iogrp_count status site_id site_name host_cluster_id  host_cluster_name 0 Win2K8 2 4 degraded 1 ESX_62_B 2 4 online 2 ESX_62_A 2 1 offline IBM_2145:ITSO_DH8_B:superuser> lshost Win2K8 id 0 name Win2K8 port_count 2 type generic mask 1111111111111111111111111111111111111111111111111111111111111111 iogrp_count 4 status degraded site_id site_name host_cluster_id host_cluster_name WWPN 100000051E0F81CD node_logged_in_count 2