2.4 Management Techniques
A wide variety of management protocols and APIs are used throughout the storage world. In addition to managing control points for a particular device, you must determine which path the control structures take to get to a particular device or software module.
Consider that you want to communicate with a particular device for two purposes: to control the device or to move data (other than control data) to and from the device. The path the control data takes is known as the control path, whereas the other data is routed on the data path. Some devices have only one network or cable connection, and both the control path and the data path are intermixed on the same cable. This is known as in-band device management; the management data flows in-band with the data. Other devices, such as managed fabric switches, separate the data and control paths; this is known as out-of-band management. An ethernet port on the switch serves management data through an IP connection, whereas a fibre channel connection is dedicated for the data path.
A heterogeneous environment is likely to use a mix of in-band and out-of-band management styles. There are reasons to use both. To make matters more complex, out-of-band management can be easily brought in-band with various types of switches, hubs, and routers.
This section discusses three management protocols that have widespread backing in the industry. Each management protocol is targeted at its own niche:
NDMP, an out-of-band management protocol for backup processes
SNMP, a generic network management protocol that is intended to manage network infrastructure components
WBEM, a comprehensive management standard for accessing data about any device or software that can be managed
A data management application (DMA)
Data management servers (DMS)
The Common Information Model (CIM): a complete modeling language for modeling managed elements and the associations between them
The CIM Object Manager (CIMOM): a location where live data adhering to a model is found
The XML over HTTP data access protocol: a generic request/response mechanism for querying and manipulating data in a network CIMOM
These two protocols and one standard give a sense of how data can be handled in a network of components. Within a complete storage network or production network, a combination of these approaches may be in use. Furthermore, many other standards and protocols are used to monitor devices and move data.
2.4.1 Network Data Management Protocol
Network Data Management Protocol (NDMP) is an open protocol that addresses the requirements of enterprise-wide network-based backup systems. NDMP is interesting because it splits the backup control path to an out-of-band control mechanism.
In traditional backup operations, the backup client not only controls the backup operation but also moves the data. Both the control and the data flow over the same network and take the same paths (in-band management). As a result, backup data and control data flow over the same network. Furthermore, this network is often the production network. The result is extremely heavy and constant traffic over the backup period, creating a negative impact on any users of the production network.
NDMP splits the task of backing up data into two pieces:
The application controls data movement. For example, the DMA would log in to a DMS across a production network and start a data movement. The DMS would be responsible for performing the data movement. The NDMP protocol defines the operations that can be carried out and the message format that must be adhered to between a DMA and a DMS.
We mention NDMP here to point out the evolution toward separating data paths from control paths. Furthermore, although many people not in the storage industry believe that backup and data movement applications are a fairly static topic, this is simply not the case. With production networks in service 24 3 7 3 365, reducing the amount of data traveling across the production network while at the same time creating a valid snapshot of data for disaster recovery is one of the true challenges that administrators face every day.
More information about NDMP is available from the Storage Networking Industry Association, http://www.snia.org.
2.4.2 Simple Network Management Protocol
SNMP is the most widely used of standard management protocols for managing network infrastructure.
SNMP works by moving data around a network in standardized management information base (MIB) structures. With SNMP, a client can read information about devices, write information to a device, or listen for alerts (events) in a network that pertain to a particular device.
MIBs are standardized by various communities that are interested in compatibility at the management level. Each MIB contains a standard header and data section followed by a place to hold extended information that may be unique to a particular vendor. For example, a standardized MIB for fibre channel attached devices was built by the Fibre Alliance and is available from the Internet Engineering Task Force (IETF). The MIB is used for a large percentage of network devices that exist on a fibre channel network. For example, every device in a fibre channel contains a unique identifier known as a world wide name (WWN). The MIB contains this information as well as information about the unit, product, ports, revision number, and more.
Unfortunately, SNMP is not used to the fullest extent that it could be on all network infrastructure components. Furthermore, MIBs are often not fully filled in, and devices conform to different versions of SNMP.
In many cases, the SNMP architecture is not fast enough to react to many problems that can occur in the block devices in a storage area network, nor does it contain enough information to manage block devices. For example, in many cases the disk transfer rate and errors that can occur far outstrip the ability to broadcast traps across a network. By the time SNMP information is received, a client may have already received corrupted data. This is not to say that many managed resources, such as routers and switches, are not adequately served in all aspects by SNMP. For the most part, SNMP's niche is in administrative-type work for network components.
We bring up SNMP briefly here to show that there are many robust and standardized mechanisms for pushing and reacting to data on a network. In many cases, a person who is knowledgeable about SNMP would see overlap with FMA. But there is no overlap because SNMP is not a pervasive standard for application programming; rather, it is a mechanism for managing certain types of network infrastructures. FMA itself sits above management protocols, and programmers will leverage many different management protocols to create their management applications. A person writing a management application using FMA would most likely have to be well versed in SNMP to drive the FMA components that he or she builds.
2.4.3 Web Based Enterprise Management
The final management standard that we will talk about is evolving into a major force in the industry. Web Based Enterprise Management is a comprehensive management standard that applies to all manageable resources that are available in a network. The complete WBEM standard has several aspects:
Here's an example of how WBEM is used.
A vendor creates a hardware device, such as a RAID.
The vendor models the RAID and all its components using CIM and the modeling language that CIM provides. The model includes the hardware and software and the relationships between those entities. For example, a model may show physical disk drives, a logical volume, and an association between the volume and the disk drives that are used for data that is stored in the logical volume.
The model is imported to a CIMOM, providing the CIMOM with information about the properties, associations, and methods that are available on the particular device.
The CIMOM is populated with "instances" of static data.
Data providers are attached to the CIMOM for any data that may change dynamically as the result of the hardware state. An example of such data is the temperature of a fan on the RAID device.
Clients request data from the CIMOM via a port that the CIMOM has open, much like a Web server. The format of the request is an XML data stream that contains requests for data. The CIMOM retrieves the requested data from the static data store or from the dynamic data provider and then returns the data to the client.
WBEM is really meant to be a one-stop shop for virtually any data about a device.
Again, as with SNMP, the question arises: How does FMA fit with the broad WBEM specification? A simple comparison is that of a database compared with a Web-based storefront for a retailer. One is a location to retrieve information about products, and the other is a user-friendly way to access the data. The database is provided by a database vendor, and a variety of programming and scripting languages are used to build applications to manipulate that data. A similar comparison can be used for FMA and WBEM. FMA fits a component framework over a network data repository.
It is also evident from WBEM's early uses and implementations that, like SNMP, it will probably be only one standard that is used underneath a comprehensive management application. FMA provides a way to unite the many standards that must be used to manage a complete heterogeneous network.
Systems management is clearly a huge problem that results from the explosion of heterogeneous networks. WBEM gives us a reference point for how the industry is trying to standardize management tasks as well as for how FMA fits into these standardization efforts. You will see more references to WBEM throughout this book. More information on WBEM can be found at the Distributed Management Task Force Web site at http://www.dmtf.org.