1. Field of the Invention
The present invention relates to the storage system for archiving, and more specifically to the Network Attached Storage (NAS).
2. Description of the Related Art
A Write Once and Read Many (WORM) storage is a storage that is not erasable and rewritable, but can be read freely. Currently there are two types of WORM storage systems: the volume-level WORM storage system and the file-level WORM storage system. A volume-level storage system is operative to prohibit write access from host computers to a volume of information that is assembled as a data unit group, such as a block, for a certain period of time. The volume of information may be defined and specified as a logical device. This type of system is often used as a block-level access storage system, like those communicating with hosts using SCSI, FCP-SCSI or iSCSI protocols.
A file-level WORM has a means for prohibiting write access to each file, which may be considered a data unit, for a certain period of time. This type of system is often used as a file-level access storage system, such as a network attached storage (NAS) system, which communicates with hosts using file level access protocols like NFS, CIFS, etc.
Some storage systems allow both the file-level access and the block level access. U.S. Pat. No. 6,779,083 discloses a storage system having a block interface (e.g. Fibre channel) and a file interface (e.g. NFS or CIFS via Ethernet), and allowing access to a volume from both the block interface and the file interface. Even if such a storage system has means for prohibiting write access to one of the files for a certain period of time, the file still may be overwritten from a host connected to the block interface since the volume where the file is stored can also be accessed from the block access interface. One method for preventing write access to the file is to apply a volume-level WORM function to the volume. But when the volume-level WORM is applied, write access to all files are prohibited, including those that users want to have write access.
Therefore, it would be desirable to provide a method for write protection in the system having both a block interface and a file interface.