Tape management in a storage networking environment

Today, the paradigm shift in storage architectures from direct-attached storage to storage area network and network-attached storage, and to emerging standards such as iSCSI, has a strong impact on the requirements for storage management software. The managed storage resources could be disks (from a few disks to a large disk subsystem) or tapes (from a single tape drive to large automated tape libraries). A key challenge in this field is the management of removable media such as tape, optical, or others. Besides having to keep track of a potentially enormous number of different volumes and maintaining records of important attributes such as media owner, age, I/O errors, media-pool affiliation, and much more, the open storage networking environment raises new questions. In a scenario in which the use of SCSI devices is no longer restricted to a small number of locally attached servers, security and robustness become increasingly important issues. Access conflicts must be carefully controlled, mount operations have to run in a robust manner, and it is mandatory to comply with a security concept that protects data as well as privacy and confidentiality. This paper concerns the new requirements for tape management systems in storage networking environments. It describes the challenges and relates these requirements to the standards that exist todayTape storage remains a fundamental part of today's corporate data centers. It is well established as a backup medium because of its low cost per megabyte and its inherent reliability. However, applications and operating systems that use tape must support a wide variety of tape drives and libraries. The lack of an industry standard that isolates host applications and operating systems from tape hardware means that each new technology requires adaptations to existing software. The paradigm shift in architectures from direct-attached storage (DAS) to storage area network (SAN), network-attached storage (NAS), and emerging standards such as iSCSI1 compounds the requirements for technology changes and upgrades.

Instead of storage hardware being directly connected to a computer system, storage devices and hosts are now connected to separate storage networks interconnected by routers and switches. The fact that each host may potentially access each storage device increases the complexity and affects the requirements for storage management software. With the enhanced flexibility and scalability provided by storage networks, customers now have a strong demand for

* Centralized resource management that provides secure sharing of tape resources among multiple heterogeneous applications, enhanced access control mechanisms, an enterprise-wide repository for removable media, and policy-based media management.

* Platform and operating system independence to work with existing computer systems from multiple vendors.

* Application independence to provide media management functionality for a wide variety of applications.

Currently, at least two industry standards address most of these problems and are gaining widespread acceptance:

* IEEE Standard 1244 for Media Management Systems [1].

* The Common Information Model (CIM) [2] developed by the Distributed Management Task Force (DMTF) [3] and the Storage Networking Industry Association (SNIA) [4].

This paper outlines the main requirements for tape management systems in SAN environments and discusses how these standards address customer requirements.

Managing resources in a SAN

Without storage resource management software or without the explicit use of subsystems that support virtualization of resources to overcome the need for software management of shared hardware resources, any application running on any host may access any storage hardware connected to the same SAN in an uncoordinated manner. Coordinating shared access and enforcing access-control mechanisms for tape media, tape drives, and tape libraries are among the most important problems addressed by media-management software.

Robust storage management capability is commonplace in the mainframe world, where products such as the Computer Associates CA-I** and the IBM DFSMSrmm have provided enterprise-class media-management functionality for years. Now the challenge is to bring this mainframe-class media management to the heterogeneous open-systems world.

Media and drive device sharing

Typical storage networks provide physical access control by using techniques, such as logical unit number (LUN) masking or zoning, that enable, disable, or limit host access to specific hardware resources. Additionally, connections to storage devices may be reserved exclusively for a particular host bus adapter that attaches a host computer to the storage network. Because all applications running on the same host may have shared access to the same connection, all applications may potentially share the same storage-and frequently will contend for it at the most unfavorable time in the most unfavorable way. For block-based disk storage accessed through a file system layer, this might not be a problem. Here, the file system, together with the operating system, takes care of ownership and access rights and maps all of the blocks of data representing a file to physical disk storage. But tape storage is not usually accessed in this manner, especially not in the open-systems world. In a worst-case scenario, one application is used to sequentially write data to a tape, while another application is used to rewind the tape afterwards and, when called upon, overwrite it. Without access control mechanisms, any program is allowed to read data from a tape just because the tape is still mounted in a tape drive