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Fighting Corruption with Alsoft’s DiskWarrior

If you’re going to get excited about a software application, it probably won’t be about a disk utility program. There are simply too many cool games, graphics applications, and action-packed accounting programs to tickle your fancy, compared to a small selection of products whose main function is to check the integrity your hard disk – and, after all, you didn’t buy a computer just to spend time maintaining it. Nonetheless, disk utilities help ensure your Macintosh runs as it is intended, which in turn enables you to spend more time playing cool games, creating eye-popping graphics, and even balancing your checkbook.

When Alsoft introduced DiskWarrior several months ago (see "Alsoft’s DiskWarrior Combats Directory Damage" in TidBITS-457), I was curious why someone would develop another disk utility program. Symantec had updated Norton Utilities to version 4, MicroMat stayed in the fray by adding directory fix-it routines to its TechTool Pro product, and even Apple had pumped up the simplistic Disk First Aid into a more robust tool available for free with the Mac OS.





After spending a few months with DiskWarrior, I now understand the product and believe in it. So here’s the story.

Enter the Warrior — Without diving into HFS, HFS Plus, allocation blocks, or other low-level disk terminology, I like to describe the Mac OS file system’s basic function as being similar to the table of contents in a book. Just as a table of contents indicates where each chapter and page are located, the Mac’s directory structures track the locations of your files. These structures are divided into several pieces which record how many blocks are in use, the number of fragments a file has been split into, as well as where each fragment is stored. These structures have intriguing names like the Master Directory Block, the extents directory, and the ever-popular popular catalog b-tree. (See Geoff Duncan’s "All About Macintosh Extended Format (HFS Plus)" in TidBITS-414 for more details on how Macintosh disks are organized and how HFS Plus volumes work.)


Most disk utilities operate in a similar fashion, scanning your hard disk, examining the various directory structures, and making their best guess at what needs to be fixed. When these utilities attempt to repair a problem, they write permanent changes to the disk’s directory. Most of the time, these programs fix whatever problem they identify, but sometimes errors occur, the programs mis-identify a problem, or fix a problem in such a way that it creates others. In a worst case scenario, repair efforts might make the disk inaccessible, or fix the directory to the point where it’s empty and all your data is seemingly gone!

Come Out and Play — DiskWarrior takes a different approach than other commercial disk utilities. Rather than being a potpourri of specialized programs and features, DiskWarrior offers only two basic functions: recovering data and optimizing directory structures to improve performance. DiskWarrior features the most simplistic interface of any disk utility on the market – in fact, it recently took home multiple honors from the Apple Software Design Awards, including one for its user experience.


Instead of crawling through the data on your hard disk in an attempt to identify and correct problems, DiskWarrior tries to build a completely new directory for your disk, using every last iota of information it can discover about your disk, its files, and how they’re organized. This holistic approach to rebuilding a drive’s directories can yield significantly different results than a utility which merely attempts to correct directory damage, one item at a time, as it moves through your disk’s directory structures. If you like the results of DiskWarrior’s reconstructed directory, DiskWarrior can use it to replace the damaged directory on your disk; you can also use DiskWarrior for preventative maintenance, both optimizing your directory and identifying small problems before they blossom into full-fledged disasters.

When you launch DiskWarrior, a single window displays a pop-up menu, enabling you to choose which drive or volume to rebuild. The window also displays information on the drive’s file system, bus location, and status. That’s about it.

After selecting a disk to rebuild, DiskWarrior starts a ten-step process of creating a new directory, reviewing your disk’s directory structure, and optimizing the catalog. This is an extremely fast process: the program took roughly three minutes to scan a severely damaged 4 GB hard disk on a PowerPC 603e-based StarMax Macintosh clone I used for testing. Once the scanning is complete, DiskWarrior displays a report of any problems it discovered. At this stage, DiskWarrior has already built a new directory, but hasn’t made any changes to your hard disk. If you plan to use DiskWarrior in conjunction with another drive utility, it’s important to use DiskWarrior first, since you can get to this point and reap most of its potential benefits without altering anything on your disk.

Wait – how can DiskWarrior help you without making changes? DiskWarrior’s best feature is its Preview, which lets you see and interact with the contents of your drive before writing directory changes to the disk. DiskWarrior accomplishes this feat by mounting a kind of virtual disk on the desktop, which is locked to prevent writing. Not only are you able to see the contents of your drive, but you can also test the functionality of the new directory by launching programs and opening files. Most importantly, you can rescue your data by copying it to another storage device. In some cases you may not need to go any further with DiskWarrior: simply copy off those one or two critical files you can’t live without, then attempt to reformat the disk.

Just before submitting this review, one of our backup servers crashed – it’s a Power Mac G3 running Mac OS 8.5.1 with a 24 GB disk array, using four 6 GB drives with Conley’s SoftRaid driver software. The server didn’t contain critical data when it went down, so just for the heck of it we tried running the latest versions of Norton Utilities and Apple’s Disk First Aid on it. Norton Utilities’ Disk Doctor didn’t recognize the array; it merely saw each drive individually on the SCSI bus. Disk First Aid was able to work with the array but could not fix the severe catalog damage.


Then we tried DiskWarrior. The program recognized that the drives were striped together in an array. After pressing the Rebuild button and waiting a few minutes, we previewed our new directory – all our files were back. The whole process took about fifteen minutes and DiskWarrior performed flawlessly, doing what the other programs could not.

Optimize from the Inside Out — Most disk utilities include an application to defragment your hard disk and eke out performance improvements. These programs work by locating the various file fragments scattered around your hard disk and reassembling them into a group of contiguous blocks. This helps speed up access to files and programs.

Here again DiskWarrior takes another path. Instead of defragmenting the files on your disk it concentrates on optimizing the disk’s directory. Other optimization programs defragment the catalog b-tree and extents files, but DiskWarrior makes improvements by changing the tree structure itself. On a healthy hard disk, you simply have DiskWarrior rebuild the disk’s directory structure, just as you would if you were attempting to recover missing data. Speed addicts that crave even an smidgen of improvement may get enough of a hit from DiskWarrior to make the program worthwhile.

Just Directory Assistance — DiskWarrior assumes any problems you have with a drive will manifest themselves as errors in the drive’s directory structures – and for the most part, this is a good assumption. Software crashes, power outages, and forced restarts are all-too-common events in the lives of most computer users, and they in turn are all-too-common causes of directory damage.

By focusing solely on directories, however, DiskWarrior doesn’t pay much attention to the rest of your disk. If your disk were a book, DiskWarrior checks, confirms, and creates an elegant new table of contents, but it can’t paw through every page character by character looking for a particular sentence. Given the life spans and reliability of today’s storage devices, DiskWarrior’s approach is fine in many cases. However, if the data region of your disk is damaged – perhaps due to failing media, a misaligned mechanism, deficient components, or physical damage from a fall or other impact – DiskWarrior won’t be able to identify and repair a problem. Physical damage is more prevalent in removable media like Zip cartridges, but it can happen with any storage device. Searching the contents of a drive for fragments of a document is arduous work, but it’s sometimes easier than re-writing a thesis or re-acquiring key data. Other disk utility packages offer these types of low-level tools, and many hard disk formatters and disk optimization programs can perform surface scans of disks, looking for signs of physical damage. And remember, despite the reassuring claims of manufacturers, the failure rate of all storage devices is 100 percent: it’s just a question of how soon the failure will occur.

The Final Fix — DiskWarrior is an excellent utility if you experience frequent crashes, or maintain Macs for users who have problems with software errors or data loss. DiskWarrior’s greatest assets are its preview function, the speed of the rebuild feature, and the simplicity of its interface. DiskWarrior is a very capable program that can recover drives where other utilities fail, and deserves a place in your utility arsenal.

DiskWarrior is available electronically from Alsoft for $70, and on CD-ROM from a variety of resellers. The DiskWarrior CD-ROM features system folders with Mac OS 7.6.1, 8.1, and 8.5.1, and some nifty prestidigitation from the folks at Alsoft enables you to use this CD-ROM as a startup disk on any system that supports booting from a CD-ROM drive (this ranges from at least the SE/30 all the way to the most recent iMacs and blue and white Power Macintosh G3s). DiskWarrior requires a system with a 68020 processor or better (including all PowerPC-based systems) and System 7.1; DiskWarrior needs Mac OS 8.1 or higher to rebuild HFS Plus disks.

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