Know more About On Data networks, voice networks and storage networks, Storage sharing, Disk storage pooling, Dynamic tape library sharing

Know more About On  Data networks, voice networks and storage networks, Storage sharing, Disk storage pooling, Dynamic tape library sharing

Today we can differentiate between three different types of communication networks: data networks, voice networks and storage networks. The term 'voice network' hides the omnipresent telephone network. Data networks describe the networks developed in the 1990s for the exchange of application data. Data networks are subdivided into LAN, MAN and WAN, depending upon range. Storage networks were defined in the first chapter as networks that are installed in addition to the existing LAN and are primarily used for data exchange between computers and storage devices. In introductions to storage networks, storage networks are often called SANs and com- pared with conventional LANs (a term for data networks with low geographic extension). Fibre Channel technology is often drawn upon as a representative for the entire category of storage networks. This is clearly because Fibre Channel is currently the dominant technology for storage networks. Two reasons lead us to compare LAN and SAN: first, LANs and Fibre Channel SANs currently have approximately the same geographic range.

Second, quite apart from capacity bottlenecks, separate networks currently have to be installed for LANs and SANs because the underlying transmission technologies (Ethernet or Fibre Channel) are incompatible. e believe it is very likely that the three network categories – storage networks, data

networks and voice networks – will converge in the future, ith TCP/IP, or at least IP, being the transport protocol jointly used by all three network types. We discussed the economic advantages of storage networks over Ethernet in Section 3.5 ('IP Storage'). We see it as an indication of the economic advantages of voice transmission over IP (Voice over IP, VoIP) that more and more reputable network manufacturers are offering VoIP devices.

 STORAGE SHARING

In Part I of the book you heard several times that one advantage of storage networks is  that several servers can share storage resources via the storage network. In this context, storage resources mean both storage devices such as disk subsystems and tape libraries and also the data stored upon them. This section discusses various variants of storage device sharing and data sharing based upon the examples of disk storage pooling dynamic tape library sharing (Section 6.2.2) and data sharing (Section 6.2.3). 6.2.1 Disk storage pooling Disk storage pooling describes the possibility that several servers share the capacity of a disk subsystem. In a server-centric IT architecture each server possesses its own storage: Figure 6.4 shows three servers with their own storage. Server 2 needs more storage space, but the free space in the servers 1 and 3 cannot be assigned to server 2. Therefore, further storage must be purchased for server 2, even though free storage capacity is available on the other servers.

 Disk storage pooling

Disk storage pooling describes the possibility that several servers share the capacity of a  disk subsystem. In a server-centric IT architecture each server possesses its own storage: Figure 6.4 shows three servers with their own storage. Server 2 needs more storage space, but the free space in the servers 1 and 3 cannot be assigned to server 2. Therefore, further storage must be purchased for server 2, even though free storage capacity is available on the other servers.

In a server-centric IT architecture the storage capacity available in the storage network can be assigned much more flexibly. Figure 6.5 shows the same three servers as Figure 6.4. The same storage capacity is installed in the two figures. However, in Figure 6.5 only one storage system is present, which is shared by several servers (disk storage pooling). In this arrangement, server 2 can be assigned additional storage capacity by the reconfiguration of the disk subsystem without the need for changes to the hardware or even the purchase of a new disk subsystem. In Section 5.2.2 ('Implementation-related limitations of storage networks') we dis- cussed how storage pooling across several storage devices from various manufacturers is currently (2003) no simple matter. The main reason for this is the incompatibility of the device drivers for various disk subsystems. In the further course of Chapter 5 we showed how virtualization in the storage network can help to overcome these incompatibilities and, in addition, further increase the efficiency of the storage pooling.

 Dynamic tape library sharing

Tape libraries, like disk subsystems, can be shared among several servers. In tape library  sharing we distinguish between static partitioning of the tape library and dynamic tape library sharing. In static partitioning the tape library is broken down into several virtual tape libraries; each server is assigned its own virtual tape library (Figure 6.6). Each tape drive and each tape in the tape library are unambiguously assigned a virtual tape library; all virtual tape libraries share the media changer that move the tapes cartridges back and