The contents of an iSCSI LU are controlled entirely by the client accessing the contents. The server cannot interpret the file systems or other data contained within an LU in any way. Therefore, the server has no knowledge of whether the data held within an iSCSI LU is in a consistent state. This introduces a potential problem when taking a snapshot of an LU.
For example, when a client creates a file, the client must also insert the file name to the host directory. This means that more than one write is required to complete the operation. If the server takes a snapshot after the file object has been created, but before its name has been inserted into the directory, the file system contained within the snapshot will be inconsistent. If another client were to view the snapshot copy of the file system, the client would see a file object without a name in a directory. This example provides only one possible scenario for snapshot inconsistency.
VSP One File server supports creation of snapshots of the attached storage systems with Microsoft® Volume Shadow Copy Service (VSS). Snapshots created by VSS are exported as iSCSI logical units.