Article

LAN-free backup vs. server-free backup in a SAN: Part 2

John Merryman
Table of Contents

1.

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Introduction
2. Industry standards review
3. Architectural considerations
4. Server-free implementation considerations
5. Conclusion



Industry standards review:
First it is important to distinguish between the standards behind LAN-free and server-free technologies. LAN-free utilizes Fiber Channel standards, which were formalized by the ANSI T11 technical committee in 1994. [Reference 10] Since then, device manufacturers and software vendors have widely adopted the protocol standards. Today, disk subsystems, tape libraries, tape drives, directors, switches, routers, hubs, and host bus adapters widely support these standards.

Server-free technology currently utilizes "Third-Party Copy (3PC) which is a SNIA standard, or Extended Copy, which is a proposed ANSI-standard SCSI-3 command. It is critical to distinguish between the two, because Third Party Copy is the SNIA standard, which is used in implementations such as EMC Timefinder or IBM ESS Flashcopy, where logical units of disk are copied within like subsystems, or across SAN channels to like subsystems. No 'data mover' hardware components are required.

"The Extended Copy standard, the foundation of server-free backup implementations, will allow block level data to be moved directly between SAN storage devices, via specialized devices, such as 'data-mover' SAN devices. [Reference 3] The Extended Copy proposal currently before the ANSI T10 (SCSI) Committee is part of a major revision of the SCSI specification. It contains some significant modifications from the original 3PC proposal. As of the writing of this white paper, the ANSI specification had not yet passed final balloting, although it is expected to pass and become part of the SCSI-3 standard command set." [Reference 3]

Among other initiatives, the SNIA Backup Work Group is currently working on Extended Copy Test Plan, Extended Copy Session Management and mapping. These projects will relate directly to making Extended Copy implementations manageable, scalable, and available for open systems platforms. All of these will be integral to guiding the industry adoption and exploitation of the upcoming Extended Copy T10 Standard. [Reference 7]

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