Free tutors about Next Generation Backups, Server-free back-up

Free tutors about Next Generation Backups, Server-free back-up

Storage networks open up new possibilities for getting around the performance bottlenecks of network back-up described above. They connect servers and storage devices, so that during back-up production data can be copied directly from the source hard disk to the back-up media, without passing it through a server (server-free back-up, Section 7.8.1). LAN-free back-up (Section 7.8.2) and LAN-free back-up with shared disk file systems

(Section 7.8.3) are two further alternative methods of accelerating back-up using storage networks. The introduction of storage networks also has the side-effect that several back- up servers can share a tape library (Section 7.8.4). The use of instant copies (Section 7.8.5) and remote mirroring (Section 7.8.6) provide further possibilities for accelerating back-up and restore operations.

 Server-free back-up

The ultimate goal of back-up over a storage network is so-called server-free back-up (Figure 7.7). In back-up, the back-up client initially determines which data has to be backed up and then sends only the appropriate metadata (file name, access rights, etc.) over the LAN to the back-up server. The file contents, which make up the majority of the data quantity to be transferred, are then written directly from the source hard disk

to the back-up medium (disk, tape, optical) over the storage network, without a server being connected in between. The network back-up system co-ordinates the communication between source hard disk and back-up medium. A shorter transport route for the back-up of data is not yet in sight with current storage techniques. The performance of server-free back-up is predominantly determined by the performance of the underlying storage systems and the connection in the storage network. Shifting the transport route for the majority of the data from the LAN to the storage net- work without a server being involved in the transfer itself means that the internal buses and the I/O buses are freed up on both the back-up client and the back-up server. The cost of co-ordinating the data traffic between source hard disk and back-up medium is comparatively low.

A major problem in the implementation of server-free back-up is that the SCSI commands have to be converted en route from the source hard disk to the back-up medium. For example, different blocks are generally addressed on source medium and back-up medium. Or, during the restoration of a deleted file in a file system, this file has to be restored to a different area if the space that was freed up is now occupied by other files In the back-up from hard disk to tape, even the SCSI command sets are slightly different. Therefore, software called 3rd-Party SCSI Copy Command is necessary for the protocol conversion. It can be realized at various points: in a SAN switch, in a box specially connected to the storage network that is exclusively responsible for the protocol conversion, or in one of the two participating storage systems themselves. Server-free back-up is running in the laboratories and demo centres of many manufacturers. Many manufacturers claim that their back-up products already support server-free back-up. In our experience, however, server-free back-up is almost never used in production environments, although it has now been available for some time (2003). In our opinion this proves that server-free back-up is still very difficult to configure and operate at the current level of technology.