Tutors on Authorization for access to individual objects , Access synchronization and Access prioritization and mount request queuing

Tutors on Authorization for access to individual objects , Access synchronization and Access prioritization and mount request queuing

It is currently still common to use authorization procedures for entire cartridges only and not for their components. However, in order to be prepared for future developments, such as the 1-terabyte tape cartridge, a management system should, even now, have appropriately detailed access protection for subdivisions of cartridges such as sides, partitions and volumes. All components of a cartridge are suitable for access control. The application purpose determines whether the user receives access to a side, a partition or a volume. An authorization is always applicable to all elements of the authorized object. If, for example, the right to access a cartridge is granted, this right also applies to all sides, partitions and

volumes of this cartridge. It is not only cartridges that should be provided with access control. For example, it is a good idea to restrict applications’ access to cartridges that are still available. To this end, the available cartridges are combined into one or more scratch pools. The applications

are then granted the right to access only certain scratch pools. Usually, access control is less important here than an optimal utilization of the free storage capacity. Drives are also suitable for access control. However, here, too, it is usually the optimal utilization of the drives that is sought. An allocation of drives to certain users or applications should, however, be possible. As a result, users can be granted exclusive access to drives. Naturally, the grouping of drives is again an option here for simplifying management and increasing drive utilization.

 Access synchronization

As already mentioned several times, a library or a drive cannot receive and process several commands from various applications in parallel. Therefore, synchronization is required that serializes all commands received at the same time and forwards them to the drives one after the other. As a result of this functionality, devices can be used ‘quasi’ simultaneously, in the same way as operating systems allow a single processor to be

made available to several processes one after the other for a limited duration. This type of synchronization corresponds with dynamic tape library sharing and has already been described in Section 6.2.1.

Access prioritization and mount request queuing

Despite intelligent access control, there may be more mount requests than available drives at a certain point in time. Ideally, a system should collect requests into a request queue in this case (Figure 9.4). This queue can be available for each drive and also for each group of drives and collect all mount requests that cannot be carried out immediately. Once a drive becomes available again, the system can perform the next request and remove

this from the queue in question. In the search for the next request to be carried out, a scheduler can sometimes also evaluate the priority of requests and change their sequence accordingly. Request queues that are not bound to drives have the advantage that several free drives may be available for each new request that is taken out of the queue. The assignment of mount request and drive must be re-evaluated accordingly, taking into account utilization and priority in order to increase the utilization of the system as a whole. Depending upon realization, this can also lead to an application being again withdrawn from a drive, so that it has to interrupt the access to the tape. It should be possible to remove requests from a queue and change the priorities of requests via an administrative interface.

How to use Efficient use of the available resources and Access Control

How to use  Efficient use of the available resources and Access Control

A great advantage of the use of well-designed storage networks is the fact that the available hardware resources are better utilized. In contrast to directly connected devices, the available storage space is available to many applications and can therefore be used significantly more effectively. In the field of removable media this is achieved by the better utilization of the free storage capacity and the sharing of drives. Efficient use of the storage capacity The disk storage pooling described in Section 6.2.1 is transferable to removable media one-to-one. In this case, free storage space should be taken to mean both unused removable media and also free slots for removable media, which must be kept in reserve due to the continuous growth in data. Ideally, this takes place in a cross-library manner. To this end, all free cartridges from all libraries are managed in a so-called scratch pool (Section 9.4.6), which is available to all applications, so that the remaining free storage capacity can be flexibly assigned.

Efficient use of the drives What applies for the effective use of the free storage capacity also applies in the same way for the use of the drives. If drives are directly connected to servers they cannot be used by other servers, even if they currently have no cartridge loaded into them.

By contrast, drives in storage networks can be assigned to the applications that need them at the time. Thus, it can be ensured that all drives that are installed are also actually used. The utilization of drives can be further increased by mount request queuing. However, more time is then required to perform the mount requests in the queue. This is a typical time-versus-space optimization problem. With more drives, more mount requests can be

carried out in the same time. If, however, a lot of mount requests are not urgent, fewer drives can execute the requests one after the other. Ideally, the mount requests in the queues are prioritizable, so that urgent tasks are actually performed sooner.

 Access control

Reliable control to prevent unauthorized access to media is indispensable. Users and  applications must be authenticated. Successfully authenticated users can then be given suitable authorization to access certain resources. Authentication Users, and also applications, that want to make use of removable media management services must be registered with the system. A sufficiently strict authentication mechanism should ensure that only users and applications that have been unambiguously identified can use the system. Authorization Authorization is necessary to prevent unauthorized users from being able to view, or even change, data belonging to other users. Authorization can both apply for certain operations and also arrange access to certain objects (cartridges, partitions, volumes, drives, etc.). A successful authentication is a necessary prerequisite for authorization.

By means of an appropriate authorization, users or applications can be assigned the following rights regarding certain objects in the management system:

• generation and deleting of objects (e.g. the allocation and deallocation of volumes);

• read access to objects (e.g. read access to own volumes);

• write access to objects (e.g. addition of cartridges to a scratch pool);

• mount and unmount of cartridges, sides, partitions or volumes;

• moving of cartridges within libraries;

• import and export of cartridges;

• activation and deactivation of libraries or drives.

The use of various authorization levels allows access control to be modified according to the user's role. The following roles and activities are currently used in systems for the list serves as an example only. These roles and activities can also be assigned differently

depending upon the specific requirements.

The system administrator is responsible for:

• installation of the system

• installation/deinstallation of libraries

• user and application management

• management of disk and cartridge groups.

The storage administrator is responsible for:

• management of disk and cartridge groups

• cartridge life cycle management

• planning of the future requirements for resources.

The library administrator is responsible for:

• management of disk and cartridge groups for individual libraries

• planning of the future requirements for resources

• starting and continuance of the operation of individual libraries

• starting and continuance of the operation of individual drives.

The library operator is responsible for:

• starting and continuance of the operation of individual libraries

• monitoring the operation of libraries

• starting and continuance of the operation of individual drives

• monitoring of the operation of drives in the libraries

• manual import and export of cartridges into and out of libraries

• performance of mount/unmount operations in manually operated libraries

• moving cartridges within a library.The users/applications may:

• allocate and de-allocate volumes to cartridges

• mount and unmount volumes

• read and write volumes

• list and display volumes that they have allocated

• list and display cartridges upon which volumes they have allocated have been put

• list and display scratch cartridges, which are included in cartridge groups to which there is an access right

• list and display drives that are included in drive groups to which there is an access right.

Know more on problems and requirements related to removable media management

Know more on  problems and requirements related to removable media management

The problems and requirements relating to the integration of removable media in the storage network can be divided into two areas:

1. the management of removable media; and

2. the sharing of the associated resources.

In large environments, removable media management must be able to catalogue hundreds of thousands of media, storing not only the media and their attributes, but also accessing these media with corresponding data about errors, duration of use, etc. In contrast to hard disk storage, it is possible to store the media separately from drives, which means that the system must additionally know the location of a medium at all

times. Since this location can be a manually-managed store or an automatic library in which the cassettes are automatically located, special solutions are required that take these requirements into account. The second important field of application for a removable media management system

in the storage network is the sharing of libraries, drives and media. This sharing between several applications connected to the storage network requires corresponding mechanisms for access control, access synchronization and access prioritization. These mechanisms control who may access which hardware when, so that potentially all applications can access all resources available in the storage network. In order to be able to fulfil these requirements, there is an increasing need for management layers for removable media in storage networks. These layers link existing

applications to the hardware connected via the storage network (Figure 9.3). They control and synchronize all accesses and should remain as transparent as possible to the applications. As a central interface, this middleware should therefore be capable of managing all resources and also the sharing, i.e. the sharing of libraries, drives and cartridges by various applications. We already discussed in Section 6.2.2 the various options for realizing library and drive sharing for removable media in storage networks. As also mentioned at that point, we believe that an architecture that shields the applications from the complex internal processes during management and sharing represents the best and most promising solution.

After all, the management is familiar with all components and their interaction. Therefore, an optimal control over the use of resources can also be implemented there. Individually, the following problems and requirements can be defined:

• Resource Utilization: Efficient use of all available resources by intelligent sharing.

• Access control: Applications and users must be authenticated. Applications and users may only be given access to the media for which suitable authorization exists.

• Access synchronization: Accesses to libraries and drives must be synchronized. • Access prioritization:

Prioritization can be used if several accesses to a resource, for example a drive, are to

be performed.

• Media tracking: It must be guaranteed at all times that every medium can be found and accessed.

• Grouping, pooling: It should be possible to dynamically aggregate both media and drives into groups or pools in order to simplify management and sharing.

• Monitoring: Automatic monitoring of the system.

• Reporting: Accesses to media must be logged. Audit trails should be possible.

• Life cycle management: Media run through a life cycle. They are written, read, written again and after a certain time taken out of circulation.

• Vaulting: Management of offline storage locations.

In what follows we investigate the above-mentioned problems and requirements further.

Free Tutors on Control of the media changer SCSI and Fibre Channel interface

Free Tutors on Control of the media changer SCSI and Fibre Channel interface

Applications must be able to control the media changers in automatic libraries. To this end, these libraries are equipped with suitable interfaces, which the applications use to send commands and receive return messages. In the Open Systems environment the direct connection via SCSI or Fibre Channel (in-band interface) is the most widespread. On  the other hand, proprietary out-band interfaces tend to be used more in the mainframe

environment.

SCSI and Fibre Channel interface

Two procedures have established themselves for the control of the media changer via the SCSI or Fibre Channel FCP interface. In one case the media changer is equipped with its own controller and can be addressed as a separate device over its own SCSI target ID. In the other case the media changer shares the controller with the tape drives (Figure 9.1). Then it is either visible as an independent device with separate LUN (inde- pendent media changer) or is controlled via the drive LUN using special commands (attached media changer). As is often the case in the IT world, there are two contrasting philosophies here, that reveal their specific advantages and disadvantages depending upon the application case.If the media changer shares the same controller with the tape drive, then the bandwidth available to the drive is reduced. However, as only a relatively small number of commands are transferred and carried out for media changers, the reduction of the bandwidth available for the drive is low. This is particularly true in the Open Systems environment, where tapes are predominantly used in streaming mode. If, on the other hand, access is mainly file-based and if the files are located on several tapes, the ratio of media changer to drive commands increases correspondingly. In this case it can be worthwhile conducting the communication with the media changer over an addi- tional controller. However, both this additional controller and the additional SAN com- ponents make such a solution more expensive and involve additional management costs. The addressing of the media changer over a second LUN of the drive controller has a further major advantage in addition to the low costs. Normally, several drives are fitted in a large library. Additional access paths make it possible to also control the media changer over the second LUN of a different drive controller. If a drive should fail, the media changer remains accessible. Furthermore, drives are often provided with a redundant power supply or the controllers possess an additional port, which can automatically be used if the first path fails.

can be reached as an additional device with a different LUN over the SCSI port of the drive. Attached media changers form a unit with the drive. In order to move the media changer, special SCSI commands such as

 READ ELEMENT STATUS ATTACHED and MOVE MEDIUM ATTACHED

must be used Proprietary interfaces In addition to SCSI interfaces, further interfaces have established themselves, particularly in the mainframe environment. These interfaces offer a higher level of abstraction than SCSI and often also a rudimentary management of the media. Typically, such interfaces are out-of-band, i.e. not accessible over the data path (SCSI or Fibre Channel connection), but instead over TCP/IP or RS-232 (Figure 9.2).

The commands that are exchanged over such interfaces are generally executed by a control unit that is fitted in the library. This control unit can usually accept and execute commands from several applications at the same time, without this leading to conflicts. Likewise, additional services such as the management of scratch pools can be made available to all applications.

Free Tutors on Management features of removable media Tape libraries and drives

Free Tutors on  Management features of removable media Tape  libraries and drives

In what follows we give an overview of the most important features and terms, plus a brief explanation:

Cartridge

 A cartridge is a physical medium upon which storage space is available. A cartridge can be moved and has one or more sides. External cartridge label A label that is applied to the outside of a cartridge and serves to identify the cartridge, for example, a mechanically readable barcode. Internal cartridge label A dataset in a certain format at a certain position on the data carrier that serves to identify the cartridge. Side A physical part of a cartridge that provides storage space. A side contains one or more partitions. Tapes normally have only one side. DVDs and magneto-optical media

are also available in double-sided variants. Partition Part of a side that provides storage space as a physical unit of the cartridge.

Volume A volume is a logical data container. It serves to reserve storage space for applications on data carriers. A partition can hold as many volumes as desired. Please note that the term volume may have different meanings depending on the context it is used: in terms of the SNIA Shared Storage Model (Chapter 10) a tape volume is called a tape extent and may span multiple physical tape cartridges. In terms of back-up

software and mainframes a volume is often used synonymously with cartridge. Scratch tape A new tape without any content or a tape, the content of which is no longer of interest, and the entire storage capacity of which can be used for new purposes. Access handle An identifier that an application can use to access the data of a volume. Under UNIX operating systems an access handle is equivalent to the name of a device special file (for example: /dev/rmt0). Mount request The command to place a certain cartridge in a drive. Audit trail Audit trails consist of a series of data sets, which describe the processes that have been performed by a computer system. Audit trails are used primarily in security-critical fields in order to record and check access to data. As already mentioned, a system for the management of removable media should also be able to represent the logical and physical properties and features of a cartridge. Ideally a cartridge can consist of as many sides as desired (tapes generally have only one side, optical media often have two, holographic media could, at least theoretically, provide even more sides). Each side can hold one or more partitions, and any desired number of volumes can be allocated to each partition.

LIBRARIES AND DRIVES

Operating systems and applications that use removable data carriers must be able to deal with a large amount of different library hardware. In general, libraries possess a media changer, slots to accept cartridges, and drives with which the cartridges can be read and written. The media changer takes cartridges from the slots and transports them to the drives. In automatic libraries, the media changer can be controlled via an interface. This interface can be realized in the form of an in-band interface (e.g. SCSI) or an out- band interface depending upon the device (cf. Section 9.3.3). The bandwidth of these automatic libraries ranges from individual small autoloaders with 1–2 drives and a few slots through to large automatic tape libraries, in which one or more media changers can transport thousands of cartridges in dozens or possibly even hundreds of drives.

In addition to automatic libraries, a removable media management system should also consider manually operated libraries. In these, an operator takes on the function of the media changer and inserts the cartridges in the drives accordingly. It is thus possible to include even individual (standalone) drives in the system as a whole. Depending upon the level of abstraction, a shelf or a safe filled with cartridges and without any drives can also be viewed as a library. These libraries are also called vaults or vaulting locations. Particularly if both automatic libraries and vaults are used, it is wise to choose the level of abstraction for the management of the media so that vaults can also be handled like manual libraries without drives. This means that, for all libraries of whatever type, the same procedures can be applied for auditing (the requesting of all components, particularly the cartridges of a library), export (the removal of a cartridge from a less library) and import (the insertion of a cartridge into a library). In what follows we will consider the individual components of libraries.

 Drives

Like hard drives, drives for removable media are currently equipped with a SCSI or Fibre Channel interface in the Open Systems environment and are connected to the storage network via these. In the mainframe field, ESCON and FICON are dominant. As already mentioned, tape drives in particular can only work at full speed if they read and write many blocks one after the other (streaming). Although it is possible, and in the mainframe environment totally normal, to write individual files consisting of just one logical block to tape, or to read them from tape, different drives are necessary for this than those used in the Open Systems back-up operation. These enterprise drives have larger motors and can position the read-write heads significantly more quickly and precisely over a certain logical block.

Media changers

Media changers have the job of transporting cartridges within a library. The start and end of a transport operation can either be a slot or a drive. To this end, a library has an inventory in which all elements of the library and their attributes are noted. The media changer has access to this inventory. Like drives, media changers have an interface for the control and checking of their functions. It is normal to use this interface for requesting data from the inventory, as well as for controlling the transport operations. The following information can therefore be requested via the media changer interface:

• the number of drives and their properties (addresses, type, etc.);

• the number of slots and their properties;

• the number of cartridges and their properties (slot, label, etc.);

• the number of further media changers and their properties.

Learn more about Removable Media Management THE SIGNIFICANCE OF REMOVABLE MEDIA LIKE TAPE CD, DVD and magneto-optical media

Learn more about Removable Media Management THE SIGNIFICANCE OF REMOVABLE MEDIA LIKE TAPE  CD, DVD and magneto-optical media

Removable media is a central component of the storage architectures of large data centers The use of storage networks means that several servers – and thus various different applications – can now use media and libraries jointly. The management of removable media in storage networks is therefore becoming increasingly important. Hence this chapter describes the network based virtualization of tape libraries and other removable media resources. In the following section we first of all explain why, in spite of the ever-increasing capacity of hard disks and intelligent disk subsystems, removable media is indispensable (Section 9.1). Then we consider various types of removable media (Section 9.2) and libraries (Section 9.3), giving special consideration to media management. We then discuss the problems and requirements related to the management of removable media (Section 9.4). Finally, we introduce the IEEE 1244 Standard for Removable Media Management – an approach that describes both the architecture of a system for the management of removable media and also its communication with applications.

The significance of removable media

Articles with such titles as 'Tapes Have No Future' or 'Is Tape Dead?' keep appearing in the press. Some storage manufacturers proclaimed the end of tapes as early as twenty years ago. Then it was to have been all over in the last few years ... After all, they said, hard disks (e.g. serial ATA disks) have now become so cheap that it is unnecessary to move data to other data carriers. In our opinion (in 2003), removable media is, and will remain, an important building block in the storage architectures of data center In addition to their high capacity and low price, for many companies the fact that

removable media can be stored separately from read and write devices and thus withdrawn from direct access is particularly relevant. Viruses, worms and other 'animals' are thus denied the possibility of propagating themselves uncontrollably, as they could on storage that is continuously available online. Furthermore, with removable media a very large quantity of data can be stored in a very small and possibly well-protected area at low storage costs. WORM (Write Once Read Multiple) properties, which are now available not only for optical media but also for magnetic tapes, additionally increase security. Furthermore, the requirement for storage capacity is increasing continuously. Progress in storage density and the capacity of cartridges can scarcely keep up with the ever-growing requirement, which means that the number of cartridges is also growing continuously. For the film The Lord of the Rings alone, 160 computer animators generated and edited a data volume of one terabyte every day, which was stored to tape. At the end of the three-year production period, the digital material for the final version of the film – 150 terabytes in size – was stored on tape. In the scientific field, and also in the field of medicine and bioinformation, data volumes in the petabyte range have been handled for a long time. This immense requirement for storage space cannot be provided exclusively in the form of storage that is available online, such as hard disks. Power consumption, heat and space requirements would drive the costs of this so high that this type of storage could not currently be justified by the shorter access time. For example, the power consumption of an average 120 GB S-ATA drive is currently (mid-2003) approximately 13 Watts. An installation with 400 terabytes of storage thus has a power consumption of more than 42 kW! This corresponds with approximately the average power consumption for 120 german single family homes. A further important advantage of removable media in comparison to hard disks is their robustness. They are less sensitive to impact and a service life of up to 30 years is possible for media in the field of high-end tapes stored in the correct manner.

 REMOVABLE MEDIA

Various types of removable media are currently in use. These are primarily magnetic tapes (Section 9.2.1), optical media such as CDs and DVDs and magneto-optical media (Section 9.2.2). In these sections we are primarily interested in how the special properties of the various media types should be taken into consideration in the management of removable media.

 Tapes

Tapes have firmly established themselves as a back-up and archiving medium for large data quantities due to their very low costs per megabyte storage space in comparison to other media. However, tapes can only be accessed sequentially. The position of the head of a tape drive cannot, therefore, be chosen at will, but must be determined by the  appropriate fast-forwarding and rewinding of the tape. This movement of the tape costs

significantly more time than the movement of the head of a hard disk drive and an optimal speed can, therefore, only be achieved if as many associated data blocks as possible are read and written one after the other, i.e. sequentially. Access to back-up and archive data at will is often unnecessary. The speed at which the large quantities of data can be backed up and restored is likely to be a significantly more important factor than the random access to individual files. Back-up and archiving applications available today utilize this special property of tapes by aggregating the data to be backed up into a stream of blocks and then writing these blocks onto tapes sequentially (cf. Section 9.3.1). Such programs use an internal management system to ensure that they are capable of identifying at any time both the tape on which a file or database is saved and also the position of the start of the file or database on the tape (cf. Section 7.3.4) Today (end of 2003), the term 'removable media' is primarily used to refer to tapes and tape libraries. In almost all large data centres, tape libraries with several drives and a great many tape cartridges are used. They are currently the most commonly used medium for back-up and archiving purposes. Therefore, systems for the management of removable media are currently used primarily where tapes have to be managed and tape libraries have to be controlled. Nevertheless, in view of future developments of new storage technologies, current management systems should also support media that possess several sides and several partitions.

 CD, DVD and magneto-optical media

When writing to CDs, DVDs and magneto-optical media, a file system (e.g. ISO-9660) is generally applied. When writing to these media, the same limitations apply as for tapes, since only one application can write to the data carrier at any one time. Normally, this application also writes a large portion – if not the whole – of the available storage space. However, once these data carriers have been written, applications can access them like

hard disk drives. As a result, the applications have available to them the full support of the operating system for the read access to optical media, which is why in this case they behave like write-protected hard disks and can be shared accordingly. Magneto-optical media are generally readable and writeable on both sides. Depending upon the drive, the cartridge may have to be turned over in order to access the second side. This property makes it necessary for management systems to be able to manage a second side of a cartridge and control the changing mechanism so that

the cartridge can be turned over. Furthermore, the WORM properties must be suitably represented for these data carriers.

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.