Learning Guide

Data deduplication tutorial

by Russ Fellows

If you've decided that your data backup system can benefit from data deduplication, you definitely have plenty of choices. But first you need to figure out where and how to implement dedupe. There are several data backup products that incorporate data deduplication. Some are virtual tape library (VTL) products, others are network-attached storage (NAS) that may be used as a backup target, and still others are backup applications.

In this tutorial, we look at post-processing versus inline deduplication, disk-based backup and dedupe, and compare the popular deduplication products.

Table of contents

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A look at post-processing deduplication
>> Inline deduplication
>> Disk-based backup systems and deduplication
>> A comparison of deduplication products
>> The future of dedupe

A look at post-processing deduplication

For backup/storage administrators looking minimize the time it takes to back up their data, the best option is often to use a post-process method. This has the advantage of backing up data faster, reducing the backup window. The disadvantage of this method is that additional storage space is consumed. Backup data is sent to a temporary holding area in order to speed the backup process. Once that completes, the data is reexamined for duplicates, with duplicate data removed (some post systems start deduping before the whole backup is complete, so they may not require as much storage on the target).

Editor's Tip: It's also important to know how data dedupe impacts the recovery process -- specifically, how rapidly you can recall data for restoration. Read this article to learn about restoring deduped data.

Inline deduplication

An alternative to deduplicating data after a backup is to perform deduplication inline as data is being sent to the backup device. The advantage with this method is that no extra space is required. Another advantage is that once the data is deduplicated and stored, the process is done, and backup data may be replicated to offsite storage. With post-processing deduplication, data must be written to storage, then deduplicated at a later time, and then replicated to offsite storage. As a result, the time to complete the entire backup process -- including replicating to offsite systems -- can be longer than systems that deduplicate inline.

Editor's Tip: There are several kinds of backup products that incorporate data deduplication, and VTLs are one example. Read this article to learn everything you need to know about VTLs and deduplication.

Disk-based backup systems and deduplication

Data deduplication can dramatically decrease the amount of disk space required for backup data, while retaining the significant performance improvements that disk-based backup devices have over tape. Thus, disk-based backup targets, whether they are NAS devices or VTLs, allow these systems to deliver high service-level objectives, while remaining cost competitive with tape-based systems.

Editor's Tip: 2008 was a big year for disk-based backup and recovery. Read this article for a look at the latest disk-based backup and recovery trends.

A comparison of deduplication product offerings

There are several vendors that deliver products that incorporate data deduplication. Provided below is a comparison of vendors, products and features.

Product

Simpana 8

DDX

Avamar

DL 4000

SIR

VLS

Diligent

Vendor

Comm-Vault

Data Domain

EMC Corp.

EMC Corp.

FalconStor Software

HP Co.

IBM Corp.

Deployment type

Backup software

VTL w/ storage

Backup software

VTL appl. w/ storage

VTL w/ or wo storage

VTL appl. w/ storage

VTL appl. w/ or wo storage

Dedupe cost

Add-on

Included

Included

Add-on

Add-on

Add-on

Included

When Dedupe

Inline

Inline

Inline

Inline and post process

Post process

Post process

Inline

Dedupe location

Distributed

Target

Source

Target

Target

Target

Target

Chunk size

Variable

Variable

Variable

Variable

Variable

Variable

Variable

Access method

-

-

Hardware dependent

-

-

-

-

NAS (NFS/CIFS)

Yes

Yes

-

No

No

No

No

FC primary storage

No

No

-

No

No

No

No

FC tape storage (VTL)

No

Yes

-

Yes

Yes

Yes

Yes

iSCSI primary storage

No

No

-

No

No

No

No

iSCSI tape storage (VTL)

Yes

Yes

-

Yes

Yes

Yes

Yes

Product

HydraStor DataRedux

FAS DeDupe

Enterprise Archive

DXi

S2100 w/ DeltaStor

VTL Prime

PureDisk

Vendor

NEC Corp.

NetApp

Permabit

Quantum Corp.

Sepaton Inc.

Sun Inc.

Symantec Corp.

Deployment type

Secondary storage

Primary storage

Secondary Storage

VTL appl. w/ storage

VTL w/ or wo storage

VTL appl. w/ storage

Backup software

Dedupe Cost

Add-on

Included (No cost license)

Included

Add-on

Add-on

Add-on

Included

When Dedupe

Inline

Post Process

Inline

Both (Inline and post process)

Post Process

Post Process

Inline

Dedupe location

Target

Target

Target

Target

Target

Target

Source

Chunk Size

Variable

4 KB block

Variable

Variable

Variable

Variable

Variable

Access Method

-

-

-

-

-

-

Hardware dependent

NAS (NFS/CIFS)

Yes

Yes

Yes

Yes

No

No

-

FC primary storage

No

Yes

No

No

No

No

-

FC tape storage (VTL)

No

No

No

Yes

Yes

Yes

-

iSCSI primary storage

No

Yes

No

No

No

No

-

iSCSI tape storage (VTL)

No

No

No

Yes

Yes

Yes

-

The future of data dedupe

It is likely that over time, data deduplication will become a service and be offered as a feature in conjunction with multiple product types and deployment scenarios. Until this time, you must carefully evaluate their cost, performance and data retention goals prior to choosing a data deduplication product that will deliver the optimal benefits in their particular environment, or test the product carefully in your environment before you buy it.

Editor's Tip: Stay up to date with the latest deduplication and data reduction news. Bookmark our special section on data deduplication.

About the author: Russ Fellows is a Senior Analyst with the Evaluator Group. He is responsible for leading research and analysis of product and market trends for NAS, virtual tape libraries and storage security.

This was first published in January 2009

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