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The second methodology for mounting TimeFinder copies of remote devices entails changing an advance parameter on the ESXi host. This parameter is /LVM/EnableResignature and controls whether ESXi automatically resignatures snapshot LUNs (for example, TimeFinder copies). By default this parameter is set to ‘0’ so that resignaturing must proceed as outlined in the previous section. If this parameter is set to 1, all snapshot LUNs are resignatured when the ESXi host rescans the HBAs. In vSphere, this task is done automatically when there is some VMFS management operation. Once the parameter is set it is inevitable that any of the VMFS volumes that can be resignatured, are resignatured. It is essential when setting this parameter to be aware of all volumes that the ESXi host in question can see.
Note: If there are multiple ESXi hosts in a cluster that all have access to the same devices, the resignature and mounting occurs. This scenario is true even if only one host has the parameter set.
Note: Setting the LVM.enableResignature flag on ESXi hosts is a host-wide operation. If set, all snapshot LUNs that can be resignatured are resignatured during the subsequent host rescan. If snapshot volumes are forcefully mounted to ESXi hosts on the recovery site, these LUNs are resignatured as part of a host rescan during a test failover operation. So, all the virtual machines on these volumes become inaccessible. To prevent outages, ensure that no forcefully mounted snapshot LUNs are visible to ESXi hosts on the recovery site.
The LUNs presented previously in Figure 161 are used to demonstrate how this parameter works.
First, the parameter must be set. As this parameter is not available through the vSphere client, the CLI must be used.
Note: VMware SRM provides a way to set it in the UI.
Through local or remote CLI issue the command to check the current value of the parameter which should be ‘0’ as in Figure 174.
Now, change the value to ‘1’, which activates the setting. The command is esxcfg-advcfg -s 1/LVM/EnableResignature and seen in Figure 175.
With the setting active, once the ESXi host does a rescan, whether manual or auto, the linked target device with the VMFS volume from the R2 automatically is resignatured and mounted with the prefix snap-xxxxxxxx-. This result is shown in Figure 176.
Note: As there can be unintended consequences with this methodology, extreme care should be taken. For example, this parameter should not be used when VMware SRM is configured as part of the vCenter environment. As such, Dell Technologies recommends using the detach method.