Learning Guide

Learning Guide: SAN-based backups

While SANs can provide a world of benefits, backing up a myriad of servers to a SAN can be tricky if not approached correctly. There are a number of missteps you can make in the implementation or subsequent management of a SAN-centric backup architecture. Using a tape library and disks as a key component in the SAN can also complicate matters. Users may find questions arising with the use of different platforms and operating systems in the SAN backup process, as well as issues associated with the cost to back up multiple servers.

Here, SearchStorage.com has collected some of the best advice on the ins and outs of SAN-based backups. (Do you have other experiences or gotchas to pass along in our compilation of SAN-based backup do's and don'ts? Please

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let us know, so that we can pass them along to your peers.)

Table of Contents

  Overview of SAN-based backup techniques and differences
  Beating the cost factor of implementing SAN-based backups
  Logistics of implementing SAN-based backups
  User case studies of SAN-based backup architectures
  SAN-based backups supporting multiple operating systems and platforms


Overview of SAN-based backup techniques and differences

Five backup options to consider when implementing a SAN/NAS solution: Part 1, Part 2.
In this two-part series, Chris Poelker explains some different ways to use a SAN or NAS subsystem when you are trying to replace tape as the primary backup medium. Included among these are the use of offsite mirrors, remote tape backups and snapshots in the local SAN.

Setting up a centralized backup in a NAS and SAN
A reader new to the world of networked storage wanted to know SAN expert Christopher Poelker's advice on the best options for backing up 10 servers in one locale and 3 in another. In his answer, Poelker takes an excerpt from Chapter 9 in his book, SANs for dummies, providing a detailed listing and explanation of the merits of different backup architectural choices. These include LAN-less backup to a shared tape library over the SAN, serverless backup to a shared tape library through the SAN, disk-to-disk backup, image copy in the SAN and SAN data replication/remote backup.

Working with third party and extended copy
Chris Poelker explains for one reader the difference between the use of third-party copy and extended copy (or E-copy, X-Copy) for backups in a SAN environment.

The difference between LAN-free vs. server-free backup
In 2002, contributor John Merryman provided a useful overview of the different implementations of LAN-free vs. server-free backup. While some information has changed since then, the fundamentals remain the same. This is a great backgrounder for those new to the concepts of SAN backup.

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Beating the cost factor of implementing SAN-based backups

How to beat the high costs of adding servers to a SAN
This reader has done his homework and contacted expert Chris Poelker after he did the math and realized his proposal for a SAN to consolidate backups in his environment was going to mean a cost of roughly $8,000 to connect each server to the SAN (in this case, a Xiotech system). Yikes! While he's still a believer in the merits of a SAN, he turned to Chris to help him save the ROI in his SAN proposal from going right out the window. Chris' response? In what we've dubbed, "The doctor is in: A six-step prescription for SAN backup," Poelker describes six ways to implement a SAN backup strategy using as few servers as possible.

Evaluating the costs of a SAN-based backup strategy
Are you trying to decide whether SAN-based backup is for you? Here, regular contributor Simon Gordon gives a general definition of SAN-based backup as it compares to other backup methods: Namely, direct backup and network backups. He also dissects the capital costs, operational and soft costs to consider with all three backup methods.

SAN-based backup considerations as you scale out your SAN
While expert Chris Poelker shares the conventional wisdom of setting up a SAN with two host bus adapters (HBAs) per server, he also cautions that backups present a more complex scenario involving the need to reduce backup-related bottlenecks. As you begin to scale your SAN and add more servers per director, backups can tend to get noticeably slower. While it might be ideal to add a third HBA per server, it's also a costly proposition. Read some of Chris' other recommendations for allowing speedier SAN-based backup at a reasonable cost.

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Logistics of implementing SAN-based backups

Running tape and disk down the same HBAs
One reader was working with an integrator to install and implement a SAN-based backlup architecture, when he started experiencing strange tape media errors. He wondered about the need of a third HBA for backup servers? Chris gets to the crux of the matter by breaking down the questions you need to answer when you want to perform backup via SAN: Who's going to do it (production server or backup server)? How will you mount the LUN to back it up? Will LUN access be over the network or the SAN? Do you have to back up offline, or can you do it online?

Why dual fabrics are often the way to go for SAN-based backup
Chris Poelker describes the four reasons for implementing dual SAN fabrics on a large-scale SAN. After reading his response to a reader's question, it's no surprise that he still recommends dual fabrics for SAN backups, if you don't have sufficient server slots or budget to implement a third HBA and dedicated backup path within your SAN.

Words of wisdom for backup/restore in a SAN environment
Chris Poelker describes for a reader how to do SAN-based backups to a tape library when the reader's backup server is only connected to the SAN, not the local area network (LAN). The short answer is that you can do this in the above scenario, but you'll probably need to do some fancy footwork with your LUNs and taking snapshots of data found on the other servers. There are further insights here on server-free vs. LAN-free backup.

Moving to SAN from several servers tied to DLT machines
One reader faced a logistics and management nightmare in trying to maintain the backups between several servers that were tied to several other DLT machines. Chris Poelker offered six alternatives to the reader, with one flavor or another of SAN-based backup appearing several times in the choices.

Ways to make disk and tape play nicely on the same SAN
While most folks maintain putting disk and tape on the same SAN may not always work out so well, Chris Poelker believes this is a fine option, provided you are using Fibre Channel-Arbitrated Loop (FC-AL) for the SAN fabric, and you put disk and tape on the same loop. Read what else Chris recommends in this expert answer.

Disk and tape on the same HBA? Think again.
In this tip, learn why IBM recommends using different HBAs for tape and disk connectivity and creating a separate zone on the SAN for the tape.

Backup software optimized for SAN-based backups
In part 2 of a detailed answer Chris Poelker provided on when a server is a good candidate for your SAN, he provides a basic list of the backup software vendors who offer software already optimized for use with the SAN. These allow you to back up your data directly from a disk in the SAN to a tape drive, speeding backups.

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User case studies of SAN-based backup architectures

Tape SAN gets good rating from credit analytics company
This case study explores how one credit analytics firm succeeded at reducing its backup windows substantially through the use of both a disk- and tape-based storage area network. This is no small feat, given the fact that the company's storage needs grow on average between 1-2TB per month.

Storage network centralizes tape backup
In this case study, learn how the MGM Mirage's IT department went from a decentralized tape backup operation that spanned five sites and three continents to one centralized SAN-based backup methodology. You'll learn here how they decided to grow out their initial SAN-based architecture in phases, based on the data growth needs of their enterprise.

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SAN-based backups supporting multiple operating systems and platforms

How to perform cross-platform backups to a SAN tape library
How should you engineer cross-platform backups to a shared SAN tape library? Or, should you even set it up that way to begin with? This reader asked expert Chris Poelker if there was any reason for not sharing AIX, Solaris and NT2000 to the same tape drives in a SAN fabric as long as they were zoned to see the tape drives but not each other? Among Poelker's advice here was, "He who controls the robotics, controls the library." Poelker also discusses the appropriate use of taking image copies in this scenario.

How to make SAN-based backup work for Macintosh OS workstations
Chris Poelker tells one reader how the purchase of a data router (or Fibre-to-SCSI bridge) is all that's needed on the hardware side, at least, to connect an existing tape library to their new SAN. However, supporting the software side of SAN-based backups for Macintosh workstations and servers may take a little more research to track down the appropriate set of tools.

How to back up Netware systems to the SAN
While this reader was trying to figure out how to back up his Netware systems using a Compaq StorageWorks SAN at the time, Chris Poelker's response still stands the test of time. Included in this gem is Chris' advice to use SAN-based "clones" of the production volume for back up to Netware, and to create a mirrorset on the array you want to be able to back up. Chris goes on to suggest a couple of CLIscripts for automating the creation (and breaking off) of a mirrorset.


Do you have questions on SAN-based backups for our networked storage experts? Ask them here.

This was first published in November 2003

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