Backup So Easy Even Your Users Can Do It

Is your valuable data left unprotected in remote users' hands? The keys to a successful strategy are simplicity and convenience. Our primer will help get your remote-user backup program off

June 10, 2004

27 Min Read
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On the other hand, removable storage, such as external hard drives, are always accessible to the user and can transfer data at a much greater rate than almost any network connection. The downside: Removable storage is almost entirely dependent on the user to manage, and travelers won't like the extra load. You also must make sure the backup device and/or media are carried separately from the user's computer.

Storage Requirements: What To Keep

A major consideration when evaluating remote backup schemes is whether you need to back up the full system or save only user data. A full backup of Windows XP and basic productivity tools consumes more than a full gigabyte, even when compressed. A My Documents folder usually holds a fraction of that once you remove unnecessary music and graphics files. There are exceptions, such as PowerPoint documents, video sales presentations or even database files that might be needed on the road. Fortunately, many of these large files do not need to be updated frequently and can be distributed easily on any type of writable media.

Another factor to consider is whether a full backup is of any value to an average user whose computer has been lost or stolen. Most won't be able to handle a system build and full restore without assistance, even if he or she could find exact replacements for the lost laptop. In the time it would take for a remote user to locate a suitable replacement computer, download a full backup and install and troubleshoot the software, an IT team could arrange to overnight a completely loaded system, including any recently backed-up documents resident on a corporate server. The main focus of a remote backup plan should be protecting data files that users commonly modify.

Usability contributes directly to the success of any backup strategy. Face it, if the process is complex, time-consuming or inconvenient, it won't be done consistently. The best hope for compliance lies in making the whole enchilada invisible to the user.This can be a challenge, especially when taking a local-storage approach that may involve connecting a device to the computer or inserting media and initiating a backup that may prohibit other work. The task can be shortened by an incremental or differential backup, which writes only files that have changed since the last backup, but for the most part a local storage backup remains user initiated.

Online backup, whether to a service provider or to your server, can occur whenever the user connects to the Internet, either through user initiation or by schedule. The level of complexity varies substantially between software packages and services, but all remote-backup packages minimize backup time through compressed incremental backups. In addition, many online clients are designed for low processor utilization to allow background execution while other work is in progress.

The time required for a remote backup depends on how extensively the data has changed since the last backup, the connection speed and the degree of data compression. The initial backup will take the longest--possibly hours depending on data volume, even when attached directly to the local network. Estimates of typical online backups range from two to 10 minutes on a broadband connection, but may take 10 times longer over a dial-up connection. Fortunately for dial-up users, all the products we examined are designed to handle and resume interrupted transmissions, so a backup routine may span more than one connection period.

Data Security: Mum's the Word

Security for the mobile backup can be addressed at several levels. Online, the first level is at login, using a secure authentication mechanism with passwords or digital certificates. The second is during transmission, using data encryption in the event you need to send over an unsecured connection. The third level of security encrypts data at the server or storage level (see "DB Confidential,").You can also use encryption for direct-connected backup, and password-protected encryption is available with most backup software packages. In the end, the password you choose must be complex--if someone gets control of your physical media, he or she may attempt to perform a dictionary attack against your password. The amount of encryption you use is based on your company policy and may be dictated by specific legal or government-mandated security standards.

"Data storage is always a short-term process," says Bruce Schneier, CTO of Counterpane Internet Security. "In the normal course of business, you won't need to store data long enough to worry about the encryption algorithm being broken. There are many more weaker links." These include poorly written programs that control access to data and personnel malfeasance issues, such as employees intentionally selling or sharing company secrets.

Administration: Getting a Handle

A corporate-centric model offers the most IT control over the backup process by providing reporting, storing data on company servers, and in some cases supporting content-push capabilities and centralized resource management. Some online backup services provide similar reporting and file-distribution options and are IT-friendly. Local-media systems remain the responsibility of the user.

Regardless of the method, the success of your remote backup depends on user cooperation. Sadly, the standard IT philosophy ("If they don't back up, it's their own problem") won't hold up if you're called to explain how that attitude fits with your company's expensive disaster-recovery program.The main goal is to protect mobile files. Don't let that goal become so eclipsed by IT control issues that nothing gets done.

Most large companies have secure offsite backup and disaster-recovery plans, but they probably don't address the needs of the single or remote desktop, mainly because these systems are not an issue in the typical client/server network storage model.

Support for the remote/mobile user is an emerging market segment, so the logical place to start investigating integration is with your backup vendor. Even if your provider has yet to address this new category, your software may offer remote users a viable short-term solution.

The idea of seamlessly merging this new backup responsibility with your existing methodology is attractive but may not be possible, practical or cost effective. Simply getting this issue on the IT radar screen for planning is an important step, and at the very least you can ensure that your interim remote backup system will be compatible with your future plans for enterprise backup.

Cost: The Final FrontierCost might be at the top of your list, but we're mentioning it last because investing in backups is a lot like buying insurance: ROI is tough to calculate, and it comes down to the level of risk you're willing to assume. Each strategy has its own cost considerations:

• Corporate centralized backup: Start-up costs include the base package and/or per-seat pricing, as well as the cost of additional enterprise storage. Savings may be seen in reduced support costs through centralized management.

• Online backup services: No start-up costs, and ongoing expenses are based on actual usage. There's also the benefit of unlimited expansion without additional hardware investments, and the possibility of volume rates. Support costs will be relative to the level of service bells and whistles.

• Locally attached removable storage: Initial costs are for hardware and backup software, and you may see higher individual support costs. Also, consider ongoing media expenses, especially if you require duplicate or offsite media storage.

Door No. 1, Door No. 2 or Door No. 3 ...Think of the first half of this article as "Remote Backups 101." The second half covers a representative selection of corporate centralized backup systems, online backup services and locally attached removable storage devices. Note that this is not a comprehensive review; space constraints limited us to listing only a few products in each category, and these are presented in alphabetical order. Most of the enterprise backup software vendors we spoke to for this article can handle laptop backups when attached to the local network, but we were interested only in those with tools specifically designed for remote backups. On a side note, several of these products offered interesting alternative uses for bandwidth while the remote user is attached, including software administration, asset management, file synchronization, content push and other administrative features.

Corporatewide centralized backup is the most sophisticated and manageable option. By integrating remote backups with your existing methodology, you can use existing onsite secure network storage; operate under a common management interface; use existing reporting and compliance tools; and easily provide updated versions of complex datasets, such as inventory databases. Several of the major enterprise-level backup providers that we polled offer add-on modules or standalone software tailored to the mobile user; we've compiled a sampling here:

Altiris Recovery Solution 6.0 Altiris' proprietary Redundant File Elimination technology builds a database and stores a pool of shared files common to all systems in your backup scheme. This serves as a core reference for all future backups and reduces the required amount of enterprise storage by eliminating the need to store multiple instances of system and application files. Files unique to each user's system are logged separately into the database and stored under that user's system profile.

The backup server is "seeded" with common and user-specific files through an initial (and time-consuming) full backup; future backups, which Altiris calls "snapshots," are compared with the existing database and only new or modified files are transmitted. To further reduce bandwidth requirements, file comparisons are done at a block level, and the results are compressed before transmission to the host.

Restoration options vary from a simple Web-based file restoration to a history-based rollback that can restore a damaged system to a previously known state. You also can create a hidden drive partition with a bootable Linux kernel, providing a complete local-restore capability; the hidden partition can be used for optional local backup if an Internet connection is not available.Altiris is all about systems management, so it's no surprise that its approach to data protection for the road warrior encompasses not only backup and restore but a number of management tools with reporting and administration options for the IT support team. The Altiris Recovery Solution is available as a standalone application, but it's also designed to integrate into Altiris' much larger group of enterprise applications for asset, client and server management. Licenses cost between $35 and $50 per seat based on volume; the core server software is free.

Computer Associates BrightStor ARCserve Backup for Laptops & Desktops With BrightStor for Laptops & Desktops, CA obviously is looking to make the backup process simple and transparent to the user, while offering the IT manager administrative control. The client software can be centrally configured using predefined backup templates and distributed to users through e-mail or linked to an online resource.

From the client side, the user must install preconfigured client software which, after an initial baseline backup, waits for a prescheduled or user-initiated backup. The backup client can be configured to be invisible to the user and run quietly in the background, letting other tasks continue while the agent does a byte-level comparison of files requiring backup.

If the system is online during the backup procedure, compressed changes are transmitted to the server as they're identified. If no server is available, the client will create and store a compressed data file of all the changes for transmission the next time a TCP/IP connection is detected. BrightStor also can resume the transmission of a data backup from where it left off after a disconnection, and has an agent that enables the backup of open files.

Administrators can prevent the user from interrupting the backup process or can have the agent delay the process until an idle period is detected. For restoration, history length is an administrative option, but users can restore any files they need from any time a backup was made. A limited restore from local information can be made if a network resource is unavailable.The user interface provides two levels of complexity--a simplified basic interface and one with more advanced features for those with special requirements. An administrator's GUI provides a convenient interface for account management, user database analysis and other tasks. It also offers server administration tools to manage data across multiple BrightStor servers and supports migration of data to long-term tape storage on other ARCServ BrightStor backup servers. System reports include data growth, server activity, database analysis, file migration, and backup-and-restore logs.

BrightStor for Laptops & Desktops is available as a standalone product that can be integrated with CA's enterprise backup software. Pricing starts at $490 for the base client/server applications with a 10-user license; volume licensing is available.

IBM Tivoli Storage Manager Tivoli Storage Manager is an example of an existing enterprise application that has features for mobile systems. Portions of the TSM client for Windows can be configured to provide the same level of backup efficiency, file compression and encryption as dedicated remote backup client applications.

The key to Tivoli's remote backup capability lies in IBM's ASD (Adaptive Subfile Differencing) technology. The process begins with a full backup, with subsequent backups only for changed files. What makes ASD unique is that it uses a combination of byte-level incremental, block-level incremental, local caching and selective backup methodologies to calculate a backup scheme appropriate for files of all sizes. This reduces unnecessary processing overhead when comparing small files, while effectively decreasing backup data volume on larger ones.

TSM is a massive, multiplatform data-management environment, and because of its complexity, configuring the Tivoli Windows client to work as seamlessly as some of the dedicated remote backup applications will involve a bit of work. The client supports dial-up and broadband connections and uses 56-bit DES encryption, but the backups can be run only when the system is online.The features that make remote backup viable in TSM have been available since version 4.1; the software is now at 5.2. There is no additional cost for this functionality, and the tools for managing remote systems are available in all versions of TSM version 4.1 and above. TSM licenses for laptops run an additional $65 per seat when added to existing installations.

Veritas Backup Exec 9.1 for Windows Servers, Desktop and Laptop Option Veritas offers a Desktop and Laptop add-on module for its server-based Backup Exec product. The complete package includes two main components: the Desktop and Laptop Option Administration Console, which can run on the Backup Exec media server or on any Windows system on the network, and the Desktop and Laptop Agent for client systems.

Veritas focuses on linking remote systems to an existing network share, where its enterprise backup methodology takes over. The client can run backups online or offline and can be invoked in four modes: manual as needed; scheduled at specific times; periodic (every 30 minutes, for example); and continuously, in which files are backed up as they're saved and closed.

Veritas' method differs in that it looks at mobile data as an extension of conventional network data, rather than as a standalone dataset. When the system is offline, the incremental backup data is stored in a local folder that allows users to restore recently backed up files without connecting to the server, and when the system is connected to the network, the user initiates a synchronization that refreshes the files on his or her network share.

The process of synchronizing remote data and "regular" network data lets you make files available concurrently to any network resource and is well-suited for users who need to work from a variety of desktops. Veritas uses a full file-level incremental backup scheme instead of byte- or block-level comparisons, so backup data that must be transmitted will be relatively hefty. However, the data-transfer agent is configurable to handle low bandwidth and interrupted connections, and backup data is secured through Windows user authentication as well as with optional 128-bit file-level AES encryption.Minimum requirements for the Veritas Desktop and Laptop Option is a Pentium system with Windows 98 SE or greater, and the package is available for $20 per seat based on a 100-user license.

This unique group of companies offers online backup services as well as client/server software for an end-to-end online backup system. With these products your organization can give mobile users online backup services. The data remains on your servers--a viable solution for companies whose existing backup products don't support individual desktop/laptop backup capabilities. These local-server-based offerings are specifically optimized for remote data backups that will promote compliance, yet the data is stored on local servers that can simply be added to your enterprise-level server backup scheme. Here are two examples:

Connected Corp. DataProtector The same software Connected uses to run its fee-based online backup service is available to enterprises, giving remote users data migration, data recovery, asset reporting, fast system rollback and optional e-mail handling. Connected's DataProtector licensed software with the optional EmailOptimizer costs $60 per PC based on 1,000 PCs. One pair of servers can support as many as 20,000 users, and the system is scalable to handle more than 100,000 users (for more information, see "Connected DataProtector with EmailOptimizer 7.1: Connected's Got Your Back," ).

NovaStor NovaNet-Web Like DataProtector, NovaStor's package offers the same features as its online service, providing efficient binary incremental backups, a simple Web interface, data encryption and compression, silent backup scheduling and e-mail reporting. NovaNet-Web is in use at sites with more than 60,000 users, but a five-user version is available for $695 (for more information, see "NovaStor Unveils Small-Business Backup,").

Free online storage services were a memorable part of the late 1990s Web explosion, as companies like Driveway.com, iDrive.com and MySpace.com floated comfortably on a seemingly endless sea of venture capital. Even though MySpace. com had almost 7 million users at its peak, it was swept away with most every other Web company based on a free-service business model.The implosion cast an undeserved unfavorable light on those online storage/backup providers that survived through tenacity and logical, fee-based business plans. Today, there's a resurgence in this market--a quick Web search identifies hundreds of offerings, and it was a challenge choosing which to highlight.

We picked four of the largest fee-based services that focus on server data.

There's an important distinction between online storage and online backup providers. As a rule, online storage providers offer a basic browser interface featuring "Web folders" for simplified storage, sharing and recovery of files and sometimes an optional backup client. In contrast, online backup services provide much more sophisticated backup clients that offer more security and complex backup configurations and support byte- or block-level file comparison for bandwidth optimization, along with an optional Web interface for easy file restoration.

Either type of online service could serve as an interim or primary backup option for road-warrior data. An inexpensive subscription could eliminate the need for additional local network storage and reduce support staffing requirements, while providing guaranteed secure and accessible online backups. Storage plans are extremely flexible, and it's painless to increase your total capacity if the need arises.

The main drawback to online backup may be that your company data is entrusted to an outside agency. Fortunately, most online companies have established stringent security features, including password authentication schemes that prevent anyone but an authorized user from accessing your data, and encryption that might exceed what you're using internally. Data availability may also be a concern, but most top providers promise 99.99 percent uptime through redundant data centers and mirrored servers.Connected Corp., www.connected.com We mentioned Connected's DataProtector software earlier, but the company also offers secure online backup services that are business-oriented and provide the same data and user management tools as its licensed product without the cost of servers and storage. Packages are available to suit any size organization.

Backup and restore functions are handled by sophisticated and user-friendly client software that supports block-level data comparison, redundant file control, automated backups, transaction reporting and encrypted/compressed data transfers. There are also tools for full system restoration and history-based file restoration, as well as a basic Web client for simplified file transfer from any Internet-connected computer. Individual packages range from $79.95 per year for a basic 250-MB storage plan up to $799.95 for 30 GB, with corporate pricing running about $9 per month, per user for 1,000 users.

Pro-Softnet Corp. IBackup, www.ibackup.com Since 1999, IBackup has provided a wide range of backup services, with plans for low-traffic single-user backups, medium-traffic basic storage and high-volume storage for the multiuser workgroup. The client offers subfile comparison, data mirroring, file compression, encrypted transfers, automated operation and e-mail or desktop confirmation.

Depending on the plan, an IBackup account can be set up to support more than one user, allowing for collaboration. A sub-account also can be configured to manage bidirectional FTP transfers, which would let you maintain an open file-distribution point without the accompanying security headaches on your system. Another interesting feature is that its remote drive can be mapped as a network drive in Windows, providing simplified drag-and-drop file movement. Backup-only plans start at $149.50 per year for 2 GB. Basic multiuser subscriptions cost $4,320 per year for 50 GB and as many as five subaccounts; a 500-user, 50-GB workgroup plan is available for $12,000 per year.

NovaStor Corp., www.novastor.com NovaStor's online backup service, driven by the NovaNet-Web product described earlier, caters primarily to individual users, though servers make up about 10 percent to 15 percent of its customer base. The backup agent has many of the advanced data-management features offered by other plans, coupled with a user-friendly interface. In addition to automated backup, versioned file restore, FastBit data optimization and file-compression capabilities, NovaStor's connection agent tolerates slow and interrupted data transfers and uses 448-bit Blowfish encryption.A basic backup plan costs $199.95 per year for 500 MB of online storage. And in case of emergency, NovaStor will write your data to CD-ROM and ship it to you for $24.95 per disk.

Xdrive, www.xdrive.com Since its inception in 1999, Xdrive has focused on providing users with simple and convenient online file storage and sharing services. Its optional desktop client is a file-transfer manager rather than a backup-specific tool, but users can simply log in to a basic Xdrive account using a browser. From there they can upload and download files, set up shared folders and make files available via FTP or HTTP. Xdrive also offers an expanded Workgroup account, with increased storage limits and support for multiple concurrent users.

We included Xdrive in this list not only because of its long-term popularity, but because it's an excellent example of how simple and inexpensive a remote data-backup process can be. Although this service requires more user intervention than the more sophisticated setups we've examined and doesn't offer a backup client, any type of offsite secure storage is technically a viable data-backup option. Xdrive is user-friendly--an average user can set up an account and create a sharable, secure online backup space in just a few minutes. User accounts start at $99.50 per year for 500 MB of storage and top out at $5,750 per year for a 35-GB 100-user workgroup account that supports online file sharing and collaboration.

Removable storage defined the remote backup process prior to the massive growth of Internet and networked resources. The floppy disk may be practically unknown to our newest generation of computer users, but it served us well until the introduction of reasonably priced tape drives. Today, it's almost impossible to buy a laptop without a CD-R or DVD-R internal drive, and the universal acceptance of USB and increasing availability of systems with FireWire (IEEE 1394) connections have resulted in an amazing increase in external mass storage options suitable for backups.

The main drawback is the amount of user intervention required compared to an online option. CD-R/DVD-R disks must be inserted, tapes must be changed and external hardware must be hauled around and connected.On the plus side, removable media provides an inexpensive backup method and makes the availability of an Internet connection moot. USB2.0 and FireWire connections operate at speeds over 400 Mbps, which is substantially faster than a typical Internet or network link.

Third-party backup programs for Windows, including the Microsoft backup application, support any of the removable media options listed below and, with the exception of tape drives, all support Windows-standard drag-and-drop file actions.

CD-R, DVD+/-R and Removable Disk CD-R is the new gold standard for removable storage media. Cheap, compact and easy to use, practically every PC sold is equipped with either a CD or DVD writer. With storage capacity up to 4.2 GB, there's substantial capacity for most data-only backups.

For removable options, Iomega offers external CD/DVD burners and flash media, as well as the classic Zip drive and the new REV drive. The $399.99 USB REV Drive is based on removable hard-platter technology and can store 35 GB native or 90 GB compressed data on a $59.99 cartridge.

External Hard Disk Until the introduction of FireWire, external hard disks were expensive and limited to computers with SCSI host adapters. Today, a number of manufacturers produce external USB and/or FireWire hard drive modules with capacities up to 300 GB at a cost of around $1.25 per gigabyte. There are also inexpensive external housings available that convert any 2.5-, 3.5- or 5.25-inch IDE device into a USB2.0/ FireWire device.External Tape Drives A staple in data backup, external tape drives in various formats have been available in SCSI and parallel versions for decades, and some formats can store up to 130 GB of compressed data on a single tape. The newest USB 2.0 Travan 40 Tape drive from Certance, for example, can store 20 GB native and 40 GB compressed data. List price for the drive is $469, and tapes can be purchased in 3-packs for $119.

Flash Media An interesting new option in data storage, rewritable flash memory modules, which became popular for storing images and music in portable devices, are available in a variety of interfaces and capacities. PCMCIA memory cards and USB 2.0 Pen Drives are now available in 2-GB and 4-GB capacities, can fit comfortably in a shirt pocket, and have enough storage to hold a complete image of a laptop's OS and applications as well as user data. Pricing runs from $0.40 to $0.50 per megabyte, and there are even versions that offer 128-bit encryption and/or biometric fingerprint recognition.

Your Job Here Is Not Done

Whichever route you take, you must have a support plan. The first call users in trouble will make is to your helpdesk--or maybe you--and odds are they won't have a clue what to do. We can't stress this enough: Simplicity and convenience are the keys to compliance; your backup system may need to be functional under less-than-ideal circumstances.

If you choose an online service, make sure it offers an option to recover lost passwords and allow second parties to recover files. If a user quits unexpectedly, IT must be able to retrieve business data. Even corporate centralized solutions and media-based backups that use password protection for encryption must have some sort of password administration plan, or you might find your data just beyond reach when you need it most.Above all, test your system thoroughly--and regularly. You never know if your backup is valid unless you can successfully restore that data. We've seen companies follow every rule in maintaining their backups and then run into insurmountable problems when they needed to restore.

Steven Hill owns and operates ToneCurve Technology, a digital imaging consulting company. Write to him at [email protected].

It's a dangerous disconnect: Mobile users generate some of your company's most valuable business data, yet you may not have a comprehensive remote-backup system in place. For those who are aware of the problem but don't quite know where to start, we offer a primer on getting a remote-user backup program off the ground, including details on connectivity, storage requirements, ease of use, data security, administration, integration with existing backup methodologies and cost. We also provide a snapshot of some products and services that can help.

A quick word on security: If your organization has a strong, multitiered password-management policy, you're ahead of the game. If not, you must put a plan in place, not only to protect users from themselves, but to ensure that your company's data remains accessible regardless of the circumstances.

We may not have the flying cars and personal robots we expected in the 21st century, but we're on the right track with the ClipDrive Bio USB 2.0 flash drive from Memory Experts International. This storage device combines compact size, speed and storagecapacity with easy-to-use, built-in biometric security. USB flash drives have proved their worth as mobile data repositories, and there are some units that offer password-protected partitions, but the ClipDrive Bio combines fingerprint recognition with optional 128-bit AES data encryption.

The Bio uses an integrated 128x 128-pixel/500-dpi AuthenTec AES3500 TruePrint Sensor to secure one of the two partitions available to the user. When the user plugs in the ClipDrive, his or her system automatically assigns a drive letter and mounts the public partition; installing the ClipDrive Bio application will make the secure partition available as a second drive.

Loading the software and setting up an administrator account takes only a few minutes. The device can support as many as 14 users by storing at least two fingerprints for each user in a database located on a third partition, which is invisible.

The public partition is handy for storing the setup software needed for secure support on other systems. All data stored on the device may be allocated between the public and secure partitions. Bio drives are available in 64- , 128- , 256- and 512-MB versions, as well as in 1- and 2-GB models. A 4-GB version is in the works.

What makes this device most intriguing from a road warrior's perspective is that a single, 2-GB ClipDrive Bio could conceivably hold an entire drive image of your laptop's basic operating system and applications, as well as continuing sequential backups of your data. Not bad for a device the size of a pack of gum that weighs less than an ounce.Data-transfer rates are published at 6 MBps/write and 9 MBps/read. However, our tests with a 42-MB image file came in at a mere 1.45 MBps/write and a substantial 10-MBps/read, whether we were going from the public partition or from the secure one.

Although pricey compared with devices of similar capacity, the ClipDrive Bio offers good data security, as well as a number of immunities from ESD, RF and voltage-based irregularities. All drives have an integrated pocket clip and port shield, and ship with drivers, a cleaning cloth, a lanyard, a padded belt-clip case and a nifty USB extension/minidocking station.

• ClipDrive Bio, 128-MB version, $145; 2-GB version, $720. Memory Experts International, (888) 422-6726, (514) 333-5010. www.clipdrive.com

The concept of using incremental or differential file-backup schemes to reduce backup times and storage requirements has been around a long time, no doubt because it never made sense to keep storing (and re-storing) the same information.

Unfortunately, regardless of the method used, an entire file was always stored whenever the archive bit called for a backup. As demand grew for remote backups over slower Internet connections, it became evident that we needed further data reductions.The next logical step was to develop methods of monitoring changes within files, rather than simply note that the files had changed. Developers started breaking files into small blocks that can be used as a basis for for CRC comparison. Only the blocks with changes would require backup--typically, 70 percent less data than before, though results could vary widely.

This was a substantial improvement, to be sure. However, block technology had a drawback: It wouldn't let you store less than a full block of data, regardless of the actual size of the change.

The next step was to drill down and examine byte-size changes. By handling a file as a binary string rather than a collection of blocks, products could extract byte-level differences and compile a delta (difference) file from the combined changed data of the entire backup set.

This proved to be an even smaller subset than block-level data--a 3-byte change in the data could be saved to the delta file as only 3 bytes, as opposed to a full block. The delta file of all file changes could then be compressed, sent to a server and stored sequentially. This procedure made it possible to restore or roll back files to a specific point in their backup history.

Of course, this level of file analysis required more computing power at both the client and the server end. Moreover, software had to be developed to track and manage the substantially more complex data sets and system information needed. Recognizing the limitations of a one-size-fits-all approach, IBM further refined the process, applying a combination of techniques so that files could be handled differently according to size.Today, almost every online and enterprise backup provider offers some form of subfile analysis to reduce the size of data backups for mobile users while letting you roll back data files--and, in the case of full-system backups--restore system status to a previous operational state.

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