Disk Defragmenters Demystified

These disk defragmentation tools present a trade-off between thoroughness and time required to run the programs. Both approaches can be effective.

Most people think of disk defragmentation as a process that involves gathering and reordering pieces of data files that have been scattered on a hard drive. The fragments are moved around, like the pieces in a shell game, so that each file occupies a unified, contiguous chunk of real estate on the hard drive. The process, a little like putting together a jigsaw puzzle, speeds up disk performance by allowing the drive's heads to read an entire file without having to jump back to the drive index for more lookups.

That process is called physical defragmentation. However, no disk utility on the market does that. Instead, the tools reviewed here—PerfectDisk 7, Diskeeper 9 and the Disk Defragmenter utility included with Windows XP—all defragment logical hard drives (or volumes) created by the operating system's file system.

These utilities perform a similar operation at the volume level. They also improve performance by positioning files at specific locations within the directory in order to speed up tasks such as booting and directory access. But it's only after the defragmentation utility has completed a pass on the logical volume that the disk drive subsystem (whether Fibre Channel, iSCSI, ATA or Serial ATA) uses that information to organize data stored on the physical disk platters.

The problem of disk defragmentation has been muted somewhat by the evolution of the Windows file system. Both the desktop and server versions of Windows use NT File System. Because NTFS volumes are indexed by a master file table distributed across the drive, they derive less benefit from defragmentation than NTFS's predecessor, FAT-32. However, defragmenters still improve performance, especially for machines that multitask.

Also, while both PCs and servers with direct-attached storage can benefit from defragmentation, the process is less useful for storage arrays, which split data over multiple disks and use different principles for organizing data storage (see the QuickStudy on RAID, QuickLink a7330).

Difference of Opinion

Raxco Software Inc. in Gaithersburg, Md., and Diskeeper Corp. in Burbank, Calif., have very different views of storage optimization. Diskeeper, the 800-pound gorilla in the market, advertises ease of use and the simplicity of remote, network-based administration. It advocates automated, daily defragmentation as standard maintenance.

Raxco claims that its PerfectDisk does a more thorough job in a single pass, can operate on disks with less free space and offers powerful analysis tools. Indeed, our tests show that Diskeeper does run faster, making daily use less cumbersome, while PerfectDisk is more thorough.

Raxco also touts PerfectDisk's ability to defragment all free space as well as areas containing data. Free space on a disk gets fragmented over time, just as space containing data does. However, defragmenting free space takes extra time. Microsoft Corp.'s Windows Disk Defragmenter focuses only on areas with data.

Diskeeper deliberately chooses to save processing time by not defragmenting free space. PerfectDisk tackles both but takes significantly more time as it unifies free space and consolidates files. Defragmentation time isn't the only trade-off, however. If you defragment only data on a disk that's nearing capacity and then save a file that's bigger than any available chunk of contiguous free space, the operating system will have to fragment the new file right from the get-go.

But Diskeeper product manager Michael Materie claims that splitting files into two to three fragments is not a problem in most cases. "Putting all the free space into a single chunk is only useful for some purposes—for very large files," he says.

According to Raxco CEO Bob Nolan, if you're talking about a workstation with a small hard drive that's half empty and all you're concerned about is data, then any product will defragment it. The differences between the products start emerging "as the disk starts to fill up, as severity of fragmentation increases, and as remaining free space gets increasingly fragmented," he says.

Still, Raxco's approach takes longer, and the incremental value of complete defragmentation is questionable, according to Diskeeper. It opts for a fast but good enough pass to save time. Because of the dynamic nature of storage, the drive is constantly writing and deleting files, and free space is continually changing.

Materie contends that with Diskeeper's free-space engine, "we'll do a comparable job to Raxco, but we'll do it over a period of time rather than all at once."

Head to Head

In our tests, PerfectDisk and Diskeeper turned in performances in keeping with their developers' stated approaches to defragging. PerfectDisk took about 10 minutes to defragment 3.5GB of data residing in 23,422 files on a 5GB partition, versus just under 3 minutes, 30 seconds for Diskeeper (see table). But Diskeeper left the partition with more excess fragments and files still broken up.

Windows XP's Disk Defragmenter took slightly longer than Diskeeper, at 3 minutes, 56 seconds, and it left more excess fragments but, oddly, fewer fragmented files. Also, the Windows utility left more fragments in the most fragmented file on disk.

In keeping with Diskeeper's philosophy of producing better defragging over time, we reran its product a second time on the same partition. This time the program completed quickly, in just 1 minute, 23 seconds. A second pass produced marginally better results, cutting the total number of excess fragments to 1,281. A third pass dropped that to 991.

The three products also provided very different reports, both before and after defragmentation. Disk Defragmenter's was the most sparse, with only a small text file for statistics. Its graphical display was similar to that of Diskeeper but was confined to a single line. PerfectDisk provided an extensive, nicely formatted report that was easy to save and use, but its graphical display was more difficult to read. It indicated the difference between fragmented and nonfragmented files with only a tiny white border around each graphical data block, with no other color differentiation except for type of file use.

Diskeeper's graphical report was the easiest to read, with fragmented areas in red and unfragmented ones in blue. But it provided little in the way of statistics and generally presented these in a pop-up window that didn't even have a button on it for saving the message.

PerfectDisk didn't complain about our nearly full test disk, but Diskeeper notified us during each test run that the drive was too full (it wanted to see 20% free space), and the program warned that this was a bigger problem than fragmentation.

While PerfectDisk comes out ahead on the strength of its defragging abilities and statistics-filled reports, Diskeeper runs much faster and provides reports that are easier to read. The defragging utility that comes with Windows is adequate but not nearly as effective as the other two products.

If the length of time required to defragment is critical, then Diskeeper is the obvious choice. For extreme situations and much more complete defragmentation, PerfectDisk is the clear winner. The Windows XP utility is, of course, free and better than nothing. Before making a choice, however, administrators should do their own testing using files and disk capacities that closely mirror their specific environments.

At a Glance

Diskeeper’s full-screen graphical map of disk usage (top) was easier to read than that of PerfectDisk (bottom). However, PerfectDisk generated more detailed reports.

Diskeeper 9

Diskeeper Corp., Burbank, Calif.

Price: Professional Edition is $49.50; Server Standard Edition starts at $249.95; Server Enterprise Edition starts at $999.

Diskeeper 9

PerfectDisk 7

Raxco Software Inc., Gaithersburg, Md.

Price: PerfectDisk Workstation is $39.95; PerfectDisk Server costs $239.95.

PerfectDisk 7

Disk Defragmenter Test Results

Computerworld tested PerfectDisk and Diskeeper on a 5GB Serial ATA disk drive partition containing 23,422 highly fragmented files. To challenge the programs, disk drives were filled to 85% of capacity (95%, including reserved space for the master file table). Results for Windows XP's defragmentation utility are also shown for comparison.

Fragmanted disk PerfectDisk 7 Diskeeper 9 Windows XP
Time to defrag Not applicable 10:06 3:30/1:14 3:56
Largest free space 2.8MB 115.7MB 10.9MB/12MB 6.9MB
Fragmented files and directories 1,040 1 121/110 101
Excess fragments in partition 5,166 1 1,782/1,281 1903
Size of most fragmented file 1.2MB 0.1MB 59.8MB/59.8MB 59.8MB
Largest number of fragments in most fragmented file 296 2 144/132 154
Fragments per file 1.04 1 1.08/1.05 1.08

Kay is a Computerworld contributing writer in Worcester, Mass. Contact him at russkay@charter.net.

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