If the host you are attempting to add this datastore to is part of the same cluster as the other host that has the datastore mounted, then it should mount up fine. However if the hosts are not part of the same cluster then you need to look at the article below on VMFS lun resignature, since it sounds like the host is not recognizing the VMFS volume on that lun. Call vmware support if you have any concerns about this procedure.  kb.vmware.com/kb/9453805
hello,  my problem is when i try to add the datastore, for vmware the lun seems to be ready to add and format, but it was already formated and it has some very important virtual machine on it that i dont want to loose how to add that existing datastore, is it problem of vmware or clariion, ill try to add after rescan on others esx host and the same thing, it is show but as a new lun ready to format  thanks  maynor
unable to add existing vmfs datastore - clariion and vmware 3.5 153875