TUTORS ON OPERATIONAL ASPECTS OF THE MANAGEMENTOF STORAGE NETWORKS AND Basic of CMIP and DMI

TUTORS ON  OPERATIONAL ASPECTS OF THE MANAGEMENTOF STORAGE NETWORKS AND Basic of CMIP and DMI

For the sake of completeness we will now list two further protocol standards for out-band management: the Common Management Information Protocol (CMIP) and the Desktop Management Interface (DMI). However, neither protocol has as yet made any inroads into storage networks and they have up until now been used exclusively for the monitoring of servers.

CMIP

At the end of the 1980s the Common Management Information Protocol (CMIP) was originally developed as a successor of SNMP and, together with the Common Management Information Services (CMIS), it forms part of the Open Systems Interconnect Specification (OSI). Due to its complexity it is, however, very difficult to program and for this reason is not widespread today. CMIP uses the same basic architecture as SNMP. The management information is also held in variables similar to the MIBs. However, in contrast to the MIBs in SNMP, variables in CMIP are comparatively complex data structures. Like SNMP, CMIP provides corresponding operations for the reading and changing of variables and also incorporates messaging by means of traps. In addition, actions can be defined in CMIP that are triggered by the value change of a variable. CMIP has the advantage over SNMP that it has a proper authentication mechanism. The disadvantage of CMIP is that it is very resource-hungry during operation, both on the NMS side and also at the managed device.

DMI

The Desktop Management Interface was also specified by the DMTF. It describes a mechanism by means of which management information can be sent to a management system over a network. The architecture of the DMI consists of a service layer, a database in the management information format (MIF), a management interface (MI) and a component interface (Figure 8.12). The service layer serves to exchange information between

the managed servers and a management system. All properties of a managed server are stored in the MIF database. A DMI-capable management system can access a server and its components via the management interface. The component information is provided to the management interface by component interfaces. DMI thus provides an open standard for the management of servers, but is nowhere near as widespread as SNMP.

OPERATIONAL ASPECTS OF THE MANAGEMENT OF STORAGE NETWORKS

In large heterogeneous environments the introduction of a management system appears indispensable for those wishing to take control of management costs and make full use of the storage network. For small environments, the implementation of a management system is recommended if the environment is expected to grow strongly in the medium term. Entry in a small environment offers the additional advantage that the management system grows with the environment and you have plenty of time to get used to the product in question. If the storage network reaches its critical size at a later date you will already be better prepared for the more difficult management. Because, by this time, the installed

tools will already be well known, the optimal benefit can be drawn from them. If you have the choice between standardized or proprietary mechanisms, then you should go for standardized mechanisms. Many device manufacturers have already built support for the standards in question into their products. Other manufacturers will follow this example. When purchasing new devices, the devices' support for standards is a critical

selection criterion and should thus be checked in advance. When choosing a management system you should ensure corresponding support for the various standards. It should, however, also have interfaces for the support of proprietary mechanisms. The calling up of element managers from the management console is the minimum requirement here. Only thus can many older devices be integrated into the management system. Which strategies should a management system use: in-band or out-band? This question cannot be answered in a straightforward manner since the success of a management system depends to a large degree upon the available interfaces and mechanisms of the devices used. In general, however, the following advantages and disadvantages of in-band and out-band management can be worked out. The main advantage of the use of the in-band interface is that it is available as standard in the storage network. By the use of various protocol levels (transport and ULP) a great deal of detailed information about the storage network can be read. In environments where an additional out-band interface is not available or cannot be implemented, in-band monitoring may represent the only option for monitoring the status of devices. The great disadvantage of in-band management is that a management agent connected to the storage network is required because the in-band management functions can only be

used through such an agent. This can give rise to additional costs and sometimes increase the complexity of the storage network. On the developer side of management systems this naturally also increases the development and testing cost for suitable agent software. Agent software can be used for additional services. These can be operating system-specific functions or more extensive functions such as a storage virtualization integrated

into the management system (Chapter 5). When using management agents in Fibre Channel SAN, it should be noted that they are subject to the zoning problem. This can be remedied by the measures described or – where already available – by more recent options such as fabric device management interfaces. Out-band management has the advantage that it is not bound to the storage net- work infrastructure and technology in question. This dispenses with the necessity of support for the management system by in-band protocols such as Fibre Channel or iSCSI. Furthermore, abstract data models can be implemented with SNMP-MIBs and CIM that are independent of the infrastructure. These must, however, be supplemented by infrastructure-specific data models. The fabric element MIB and the Fibre Channel management MIB are two examples in the field of SNMP. A further advantage of the use of the out-band interface is that no dedicated management agent is required in order to gain access to management functions. A management system can communicate directly with the SNMP agents and CIM providers in question without

having to make the detour via a management agent. In the event of problems with the management interface, this source of errors can be ruled out in advance. The corresponding costs and administrative effort associated with the management agent are therefore also not incurred.

A great disadvantage of out-band management is that up until now there has been no access to the operational services that are available in-band. Although this would be technically possible it has not yet been implemented. Finally, even the additional interface that is required can prevent the use of out-band management in cases where the implementation of a further interface is not possible or not desirable. Therefore, a management system should, where possible, support both interfaces in order to get the best of both worlds. This means that it is also capable of integrating devices that only have one of the two interfaces. For devices that have access to both in-band and out-band interfaces an additional connection can be very helpful, particularly for error isolation. If, for example, the in-band connection to a device has failed, then an in-band management system would report both the failure of the line and also the failure   of the device. A management system that operates both interfaces would still be able to reach the device out-band and thus trace the error to the failed connection.

 SUMMARY

In this chapter we have dealt with the requirements and the possibilities that exist for the management of storage networks. The realization of these comprehensive requirements in a management system implies a complexity that should not be underestimated. In general, storage networks impose higher requirements on management than do storage-centric IT architectures. The objective of effective storage management is the use of a central management system that is capable of integrating both the proprietary and the standardized management mechanisms of the individual devices. Both in-band and out-band management mechanisms are offered. We discussed the Fibre Channel Generic Services for the in-band management of a Fibre Channel SAN. Out-band, standardized management mechanisms are available in the form of the important protocols SNMP, CIM/WBEM

and SMI-S. Today (end of 2003) SNMP is an important protocol for the management of storage networks. As development progresses and the power of CIM/WBEM and SMI-S increases, the SNMP MIBs may gradually be forced from the market. Suitable extensively implemented CIM providers could then also supersede the in-band interface. From an operational point of view it is to be hoped that, on the one hand, the management techniques continue to be further developed in an open and standardized – and thus interoperable – manner and, on the other, that even more manufacturers feel obliged to establish corresponding standards for their devices. In the next chapter we continue the discussion of storage management: Removable media and large tape libraries are central components of large data centres and we have not covered them so far. Thus the next chapter deals with the management of removable media.