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The second methodology for mounting TimeFinder copies of remote devices involves changing an advance parameter on the ESXi host. This parameter is /LVM/EnableResignature and controls whether ESXi will automatically resignature snapshot LUNs (e.g., 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 will be resignatured when the ESXi host rescans the HBAs. Since in vSphere this will be 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, will be resignatured. It is therefore 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, even if only one hosts has the parameter set the resignature and mounting will be done.
Note: Setting the LVM.enableResignature flag on ESXi hosts is a host-wide operation and, 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. Accordingly, all of 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.
To demonstrate how this parameter works, the LUNs presented previously in Figure 176 will be used.
First, the parameter needs to be set. As this parameter is not available through the vSphere client, the CLI will need to be used.[27] Through local or remote CLI issue the command to check the current value of the parameter which should be ‘0’ as in Figure 189.
Now, change the value to ‘1’, which activates the setting. The command is esxcfg-advcfg -s 1/LVM/EnableResignature and seen in Figure 190.
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 will automatically be resignatured and mounted with the prefix “snap-xxxxxxxx-”. This is shown in Figure 191.
Note: As there can be unintended consequences with this methodology, extreme care should be taken. For example, this parameter should not be utilized when VMware SRM is configured as part of the vCenter environment. As such, Dell recommends using the detach method.