You use SnapDrive to ensure that you create consistent Snapshot copies in the event you need to restore a LUN from that copy.
Snapshot operations on a single LUN actually make a Snapshot copy of all the LUNs on the volume. Because a storage system volume can contain LUNs from multiple hosts, the only consistent Snapshot copies are those of LUNs connected to the host that created the SnapDrive Snapshot copy. In other words, within a Snapshot copy, a LUN is not consistent if it is connected to any host other than the one that initiated the Snapshot copy. (This is why you are advised to dedicate your storage system volumes to individual hosts.) Therefore, it is important to back up a LUN using a SnapDrive Snapshot copy rather than using other means, such as creating Snapshot copies from the storage system console.
Additionally, as part of the SnapDrive Snapshot copy process, the file system (NTFS) is flushed to disk and the disk image in the Snapshot copy is in a consistent state. This consistency cannot be ensured if the Snapshot copy was created outside the control of SnapDrive (that is, at the storage system console, or using either System Manager, FilerView, or rsh, or by backing up the LUN file in the active file system.)