Java Glossary : defragger

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defragger

A defragger is a utility that ensures files on disk are in one contiguous chunk. A defragger may also position files on disk so that frequently used files get prime real estate. Ideally it would order files by last access date, perhaps weighted by frequency of use statistics. It may also defrag and tidy directories and other system tables. It may consolidate free space fragments.

NT has an official defrag interface. It is extremely conservative and slow. The idea is that defraggers can safely run while other programs are running simultaneously messing up the disk. Another advantage is that bugs in the defragger are very unlikely to corrupt the disk, and system crashes while a defragger is running are also very unlikely to corrupt the disk. It would be much faster if Microsoft would implement it properly. It should buffer up several requests to move small files, and move a batch of them (or file fragments) in one single elevator seek. The interface could stay the same. It would just have some extra intelligence inside to do the moves slightly out of order, in batches.

NT Hard Disk Defraggers
Product	Strengths	Weaknesses
Executive Software Diskeeper	Defrags, free space, directories, MFT and pagefile.sys, Moves dirs to centre of the disk.	Very slow because it uses the official NT defrag interface. Makes no attempt to position files by last access date. Directory, MFT and pagefile.sys optimisation can only be done at boot time. Boot time defrag can take 15+ hours and is not interruptible. Executive Software has Scientology connections, which may cause trouble if you are in Germany. My computer is in my bedroom and it drives me nuts clicking away in the middle of the night ever since I installed Diskeeper. The only way I could get it to stop running was to uninstall it.
Mijenix (née Ontrack) Defrag Plus	?	?
O & O Defrag	Comes from Germany. Their V6 offers boot time defrag of system files and offers a rudimentary file placement scheme to speed up access to files (sorted alphabetically by name or by modification date). O & O Defrag does background processing. Even though FAT32 is not officialy support by MS on NT 4.0, O & O says that if you have the FAT32 file system driver from Sysinternals, then they will support defragmenting FAT32 partitions. They provide a free separate MFT defragger given away as is without any support.	Does not allow network scheduling. It does not support Windows 95/98 or Windows 2000. It supports NT on Intel platforms only.
PowerQuest PartitionMagic	Quick.	Not really a defragger. Squishes partitions without attempt to defrag, prior to moving or resizing them. Does not optimise at all. Can only run at boot time.
Raxco Perfect Disk 2000	Optionally compresses small files. Places most frequently modified (not necessarily most frequently accessed) files near the center of the disk and rarely modified ones near the edges, with the free space in the central band. Defrags the page file, the MFT and the directories. The scheduler lets you allows you to set a maximum run time. Only defragger to fully defrag all the NT metadata (logfile, MFT mirror, etc.)	Very slow because it uses the official NT defrag interface. It does not fully defrag free space, though Raxco claims this is a limitation of the NT defrag interface. Earlier versions often went into an infinite loop. I don't have enough experience with the new version to know if the problem has been corrected. The new version boot time defrag options always failed claiming it could not open my NTFS partition. It worked only after I scheduled a chkdsk which found no problems. Leaves many files undefragged after a single pass. The graphic display does not keep up to date consistently as it works, but it has a window telling which file it is moving so you can at least tell it has not hung. If you shut down the program by clicking × the program does not stop, it just continues in the background as a system process eating up nearly all available CPU cycles. You can avoid this behaviour by using the stop icon to stop the program, though it seems to start itself and run at odd times even when you have not scheduled it too. You can't get rid of the background service that runs all the time, however this is true of most defraggers. The partition notebook where you configure the options for how you want a given partition handled is cleverly hidden. The way you can access it is with a double click on the drive letter. If you do a defrag run, then run it again, and abort part way through, your disk will be messier than when you started. Raxco claims to have patented the idea of file placement. This is prior art and I can prove it to anyone who needs to break the patent. I posted the idea years ago on BIX.
Symantec Norton Utilities SpeedDisk	Likely bug free.	Very slow because it uses the official NT defrag interface. Does not defrag directories or the pagefile.sys file. Makes no attempt to place files optimally.
Symantec Norton SpeedDisk 5.0	Fast since it does not use the klunky official defrag interface. It can defrag the MFT, pagefile, dirs etc. without a reboot. It places frequently accessed file near the start of the partition. Moves small files into the MFT which gives them faster access and ensures they take up less space. (The downside is the MFT needs more frequent defragging.) It is very simple to run. There are no options to configure other than the names of files you want put near the beginning or end of the disk. Puts frequently/infrequently accessed/modified files is separate bands. Places the MFT, then the pagefile, then the directories, then the high access files. Norton's placement makes more sense to me. The rainbow hued analysis map changes in ways that make sense. Other defraggers seem to have no method to their actions. They appear to just as often be messing up the disk as defragging it. Norton is not perfect. It has the disturbing quality of redefining how much of each kind of file it as it progresses. It requires only one running to fully defrag the disk.	Cannot defrag the first 16 clusters of the MFT. It is quite slow when it defrags small files. Microsoft claims Symantec's online defrag of the MFT is dangerous. This could just be Microsoft getting huffy over Symantec bypassing its official klutzy defrag interface, or it could represent a true problem. If Microsoft implemented it properly, there would be no need for bypassing it. The defragger is noisier than most, sounding as if it is going to shake your disk to death.
Symantec Norton SpeedDisk, part of Norton SystemWorks 2004	Runs on many operating systems. Reputedly quicker than earlier versions.	Two different sets of utilities all on one CD, a Windows set and and NT/W2K set. For windows, make sure you manually configure a swap file with Control panel \| System \| Performance \| Virtual Memory, otherwise SpeedDisk will keep restarting, fearing writes to the temporary swap file. It moves the swap file and directories. However under Windows NT/2000/XP it does not move directory entries (on FAT partitions) and metadata files (on NTFS partitions). It leaves them where they are, calling them unmovable files, scattered across the drive. To defrag them, you would have to reformat the drive and reload the files, creating all the directory entries first.
Systems Internals PageDefrag	defrags pagefile.sys file.	Does nothing else besides defrag pagefile.sys Can only run at boot time. You can almost as easily, and more safely, defrag pagefile.sys by temporarily moving it to another partition in the control panel, reboot, defrag, then move it back, then reboot again. However you need a spare FAT or NTFS partition to do that.
Winternals Defrag Manager	defrags network drives	Was cheap. Now they keep the price secret. $19.00 USD for single station; $159.00 USD for ten station. Defrags using safe but slow MS API. It is thus not currently capable of Page File defragmentation (or of the MFT and related NTFS metadata, since these require offline defragmenting). You do not install it on each machine. It defrags via a central administrator control. 30 day trial.

The only reasonably quick and satisfactorily thorough defragger that I know of is Norton SpeedDisk for Windows 9x-FAT partitions. Norton SpeedDisk 5.0 is acceptable for NTFS, but I think with some work it could be speeded up further to handle several small files in a single elevator seek. I know of no decent ones for OS/2-HPFS or Linux-ext-2 partitions. Perhaps one could be devised that booted under its own mini-OS and defragged by copying from partition to partition handling all the major OS formats. It would then not need to worry about crashing, and could do the I/O, including the directory and FAT I/O in massive buffered chunks.

To write an efficient disk defragger, model how you tidy your apartment, better still, how Martha Stewart tidies her house.

Student Projects | defragger

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