Zero Contents Snapshot
Original Publication Date: 2002-Dec-05
Included in the Prior Art Database: 2002-Dec-05
This paper describes the key enhancement to the filesystem snapshot technology. It explains how it reduces the administrator's management task of backup data and the restoring task of its data.
Zero Contents Snapshot
Disclosed is a filesystem function that enables users to see the change histories of contents kept in backup devices that includes removable devices such as tape or CD without accessing to them actually. This filesystem keeps the change histories of only meta-data in the accessible online devices and exposes it to users in a special directory on the filesystem like a snapshot directory. But differently from the snapshot technology, the change histories of actual data, which are accessed rarely, are kept in backup devices to save the cost of local online devices. (Fig. 1)
The recent trends of storage industry is to centralize the storage management by using shared storages locating on the network such as NAS (Network Attached Storage) or SAN (Storage Area Network). By using shared centralized storages, it saves the total storage cost and further the total maintenance cost by leaving the task such as backup/restore to an administrator. While these are essential to the storage cost reduction, there are some enhancement necessities that reduces administrator's task. One of them is the managing task of huge number of backup data. Since there are no relation between backup data in backup devices and data on active filesystems, the administrator keeps the track of the relationships by using a certain software or by manually recording to a database. Even if using such tools, it is a terrible work for the storage administrator who has thousands of users. Further more, since usually those tracking information are hidden from users, users can not know which files have been taken to backup, when the backup has been taken, how many versions are kept in it and so on. Then when user encounters some troubles with files on the active filesystem that requires a restoration, the user must call the administrator and requests to restore the files by the file name or date or a certain information. It would be a terrible work for the administrator to search the requested files from millions of files. So the sharing of the backup histories to users would be required. One of the well-known way is a snapshot technology that exposes old contents in a special snapshot directory on the filesystem. But ordinarily the snapshot contents are removed from the active filesystem after backup is completed in order to save the storage space of local online device. Hardly worth mentioning, removing a snapshot also removes the relation between the contents on the active filesystem and the contents on the backup device (Fig. 2). Disclosed here is an extension of a snapshot technology to enable for the filesystem to show the change histories in backup devices.
This filesystem creates a frozen image of current file set as a snapshot technology does when backup is requested. The filesystem suspends in a moment to create a copy 'SD001' of root directory 'D000' and then resumes and creates a new special directory in the root directory to expose the list...