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Root volumes are created automatically when a virtual machine is created. Root volumes are deleted when the VM is destroyed. Data volumes can be created and dynamically attached to VMs. Data volumes are not deleted when VMs are destroyed. Administrators should monitor the capacity of primary storage devices and add additional primary storage as needed. See the Advanced Installation Guide. Administrators add primary storage to the system by creating a &PRODUCT; storage pool. Each storage pool is associated with a cluster or a zone. With regards to data disks, when a user executes a Disk Offering to create a data disk, the information is initially written to the CloudStack database only. Upon the first request that the data disk be attached to a VM, CloudStack determines what storage to place the volume on and space is taken from that storage (either from preallocated storage or from a storage system (ex. a SAN), depending on how the primary storage was added to CloudStack).