You have Symantec’s Enterprise Vault and you are running out of disk space for your Vault Store. Your server or SAN does not have many slots to add new disks. So you are in a bind.
One possible solution is to use an iSCSI storage located off the server, coupled with a software initiator on the Enterprise vault. Most of the time, the initiator is the Microsoft initiator. Thus you can very cheaply and easily get more storage. There are lots of iSCSI storage models available in the market or you are up to it, DIY.
Other niceties include, redundant or trunked iSCSI links.
Once the iSCSI storage is up, you can create the replacement volumes and replicate the Vault Store and Index over. Once that is completed, schedule a down time, shut down the Enterprise Vault Services, replicate once more to close the open files and exchange the drive letters. You will be up an running in less an hour.
If the original Vault is still online and out of disk space, you will get a warning message from EV. This will help.