dalla FAQ di diskeeper (il 'fratello maggiore' del deframmentatore di windosw):
Why won't my volume defragment completely?
This can be the result of several situations:
-If your disk volume is extremely full, there may not be sufficient free space to effectively defragment the files. Click here for suggestions on getting more free space.
-Another cause of incomplete defragmentation is a fragmented paging file. Click here for more information on how to remedy this.
-A volume that has (at one time or another) been filled to capacity may have a severely fragmented Master File Table (MFT). There is a White Paper, entitled System Performance and File Fragmentation in Windows NT, available from the Executive Software Web site that describes the causes and effects of MFT fragmentation. To view this White Paper, click here.
-Another situation that can prevent complete defragmentation of a volume is the existence of a large number of directories on the volume. See Can Diskeeper move directories? for more information.
-Yet another cause for incomplete defragmentation can be a security access situation. It is necessary for both SYSTEM and ADMINISTRATOR to have full control over a file (or the directory folder it is in) in order for Diskeeper to have access to move the file. This is because the Diskeeper service runs under the Administrator account, and System access is necessary to defragment files safely. This is a security feature that is governed by the Windows NT, Windows 2000, Windows XP, and Windows Server 2003 C2 security requirements. Click here for more information about setting file access permissions to allow Diskeeper to defragment your files.
riassumo qui brevemente:
-disco troppo pieno: impossibile deframmentare file grandi.
-file paging frammentato: sistemabile con una deframmentazione al boot-time (non mi ricordo se si possa fare anche con il defragger di winxp)
-Master File Table molto frammentata
-molte cartelle sparse per il disco: sistemabile con una deframmentazione al boot-time
-restrizioni di accesso al file.