SAN management using CIM and WBEM

Posted on June 01, 2002

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By Steve Jerman and John Crandall

Two standards may alleviate management headaches for both end users and management software developers.

One of the most daunting problems facing the storage industry is the management of multi-vendor heterogeneous storage network environments. It is a key concern for end users, integrators, and vendors. In the absence of any prevalent standards for management, there has been a proliferation of vendor-specific and device-specific APIs, resulting in end users and vendors having to use multiple interfaces to fully manage a storage area network (SAN).

Today, a SAN administrator may have a SAN network management tool, storage resource management (SRM) software, and multiple device-specific management tools. All of these tools have various management interfaces (SNMP, Fibre Channel Services, vendor-specific APIs, etc.), resulting in multiple vendors replicating development work and potentially providing inconsistent and incomplete information to SAN administrators.

A promising solution to this problem is an interoperable, open environment for storage management based on the Web-Based Enterprise Management (WBEM) standard and the Common Information Model (CIM), both of which were developed by the Distributed Management Task Force (DMTF).

WBEM ("webem") is a set of standards developed to unify the management of enterprise computing environments. The DMTF has developed a core set of standards that make up WBEM, including a data model, the CIM standard, an encoding specification using XML, and a transport mechanism using HTTP.

The Storage Networking Industry Association (SNIA) has decided to use WBEM as the basis for a standard SAN management interface. The organization has worked with the DMTF to define the necessary modeling extensions to manage a SAN and all of the storage devices in it. This work has matured to the point where the SNIA is now promoting the interface to accelerate its adoption by the industry. The SNIA believes this technology will enable efficient multi-vendor management and empower end users to successfully construct and manage multi-vendor networks.

The foundation—CIM and WBEM
CIM is an object-oriented language and methodology developed by DMTF for describing and managing enterprise computing environments. The object-oriented nature of the model allows complex environments to be described efficiently and consistently, while allowing easy extension to cover new or vendor-specific features. The DMTF has developed a specification for the CIM language and a set of models (CIM Schema).


Figure 1: WBEM encompasses an object model, an encoding specification, and a transport mechanism.
Click here to enlarge image

WBEM is an XML-based management interface using CIM. WBEM consists of three elements (see Figure 1):

  • An object model (CIM);
  • An XML encoding specification (xmlCIM), which is written in Document Type Definition (DTD). xmlCIM defines XML elements representing CIM classes and instances; and
  • A transport mechanism, (CIM Operations over HTTP), which describes how to access a CIM model using xmlCIM over HTTP.

Together, these three elements form a flexible management interface that leverages commonly used Web infrastructure. Additionally, WBEM is "future-proof" since both the transport and encoding mechanisms can be changed as new technologies emerge.

Managing storage arrays
Today's storage arrays are complicated, often consisting of hundreds or thousands of disks, multiple redundant controllers, and sophisticated software/ firmware features (e.g., point-in-time copy, mirroring, and LUN masking). All of these features need to be configured, monitored, and managed—a task that is relatively simple for a single array but increasingly complex as you add arrays from multiple vendors.

Today, each vendor supplies a dedicated device management and configuration tool for that vendor's storage arrays. This software is often integrated with enterprise management tools for centralized monitoring.

Although common heterogeneous management exists for monitoring, there is currently no equivalent functionality for configuration and control. The complexity of storage arrays and the proliferation of APIs required to control them have discouraged application vendors from adding these functions to their software.

The SNIA, working with the DMTF, recently extended the CIM Schema by adding notions of "Storage Pools" and a "Storage Configuration Service." Instead of describing the detailed configuration of the array, a more abstract, general description is used, which, in conjunction with the Storage Configuration Service, allows heterogeneous management applications to configure storage simply using concepts similar to storage virtualization. Also, the new modeling can describe the detailed layout of the storage (e.g., striping in RAID 5), which is important for some applications.

The Storage Configuration Service includes the functions needed by a generic management client for heterogeneous configuration without requiring look-up tables or other detailed knowledge of the array. The functions that this new WBEM API covers include the following:

•Passive management, allowing detailed monitoring of both logical and physical array status and configuration; and

•Active management, including:
— Storage pool and storage volume configuration and control;
— Snapshot and mirror configuration and control;
— LUN mapping and masking configuration and control; and
— Events that allow applications to subscribe to receive changes in the storage array (e.g., addition of disks and component failures).

These functions are a major step forward for heterogeneous storage administrators and offer the prospect of automatic policy-based management (e.g., service-level agreements).

Managing the fabric
Today's SAN fabrics are a collection of various devices configured together to provide an integrated network. These devices maintain discrete pieces of information, representing a "view" of the fabric, that are exposed through various management interfaces (e.g., SNMP, Fibre Channel Services, and vendor-specific APIs).

SANs have grown to include multiple switches and multiple hosts that run different operating systems with different host bus adapters (HBAs) connected to multiple storage arrays. Additionally, tape libraries are connected to the fabric. With the addition of director-class switches and link extenders connecting two fabrics over long distances, the number and complexity of devices has grown significantly.

Managing all of the devices separately is no longer feasible. It places an undue burden on the management software vendors and, ultimately, end users.


Figure 2: One of the goals of using CIM is to model the fabric as a single device.
Click here to enlarge image

Leveraging CIM, the goal is to model the fabric as a single device. The fabric can be abstracted as a system (or "cloud") providing a set of services, including routing, zoning, and security (see Figure 2). Just like a computer, a fabric logically has components. The components in a fabric include switches, ports, HBAs, and, to some extent, the hosts, storage arrays, and tape libraries. These components work together to form a fabric.

Today, the SAN management model includes:

  • Device discovery
  • Topology
  • Device configuration
  • Device statistics
  • Zoning configuration
  • Asset management
  • Software management

Abstracting the fabric as a single device offers the prospect of delivering to users a more complete view of the fabric, and allowing management software vendors to focus on delivering functionality on a more timely basis.

Conclusion
The SNIA believes WBEM is a key technology for SAN management. Designed for heterogeneous SAN and storage management, leveraging existing technologies such as XML and HTTP, WBEM can evolve as new transports and protocols come along.

Now that the CIM model supports configuration for SANs, we can now manage heterogeneous SANs using an open interface.

Vendors should support this because it allows them to innovate and not be burdened by the "plumbing." End users should be asking for this because it will ultimately give them choice and reduce total cost of ownership.

Steve Jerman is the chair of the Storage Working Group in the SNIA and also chair of the storage team at the DMTF. He is a storage management architect at Hewlett-Packard's Networked Storage Solutions organization. John Crandall is the SNIA liaison to the DMTF Technical Council and chairs the CIM work in the SNIA for Fibre Channel. He is a senior staff engineer at Brocade and is part of the group responsible for standards work on CIM/WBEM for Brocade's Fabric Access API.


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