Nas with worm function

Abstract

A network storage system accessible by a computer, including worm functions.

1 . A storage system accessible by a computer, comprising: 
 a disk drive unit comprised of plural logical devices;    a memory module which stores information about the disk drive unit;    a first controller comprised of an interface which provides a file system to the computer to facilitate access of files by the computer; and    a second controller which receives access requests from the computer, wherein:    the first and second controllers, when a write request is made by the computer, looks up in the memory module for information on a logical target device that is a target of the write request and, when the logical target device is set to unwritable, inform to the computer that the logical target device is set to unwritable;    the memory module stores a logical unit table which indicates an association between the logical target device and an allocated logical unit allocated to the logical target device;    where the allocated logical unit allocated to the logical target device is accessible by the computer using the file system;    wherein the interface:    stores a mount table indicating which logical unit is mounted to the file system and indicating whether a write in the logical unit is possible; and    stores a map table indicating an association between the logical target device and the allocated logical unit allocated to the logical target device; and    wherein the interface:    obtains a list of files that are not accessed for a predetermined period, referring to meta-information held in the meta logical units for which a first attribute is set;    creates a Universal Disk Format image containing files on the list of files;    secures a logical targeted device that is capable of storing the Universal Disk Format image;    judges whether or not any logical unit is allocated to the secured logical targeted device;    searches, when no logical unit is allocated to the secured logical targeted device, for a logical unit that is not assigned to any logical device from among logical units in which a third attribute is set, using information stored in the memory module;    obtains, when no logical unit is found that is not assigned to any logical device, information of an oldest logical unit that has not been accessed for a longest period, from among the logical units in which the third attribute is set;    unmounts the oldest logical unit for which the information is obtained off the file system;    instructs to the first controller to allocate at least a portion of the unmounted logical unit as a new logical device;    reflects a result of the allocating to the information about the map table, the information being stored in the memory module;    specifies the logical unit to store the created Universal Disk Format image in the new logical device to which the logical unit is allocated; and    sets information on the new logical device that stores the Universal Disk Format image to unwritable, the information being stored in the memory module.