How large a partition can Diskeeper defragment?
The size of a partition doesn't really matter to Diskeeper. Some Diskeeper users have arrays in excess of 32GB which defragment fine. The critical aspects are the number of files, the percentage of free space, files that are opened exclusively, and directory files.
The more files there are in a partition, the longer Diskeeper will take to complete a pass, simply because there are more cycles to go through. Diskeeper does certain steps on each file regardless of its size. A 10KB file takes almost as long to defragment as a 10MB file.
If a partition has less than 20% of free disk space, the I/O performance will degrade noticeably, regardless of any fragmentation issues. Even if all files are contiguous, increasing the amount of free space from, say, 10% to 20% should give you noticeably faster I/O. In fact, performance begins to degrade at about the 50% mark, but below 20% the degradation is much greater. Diskeeper will also slow down noticeably when free disk space drops below 10% and may not be able to defragment, because it needs large contiguous free spaces to defragment large files. If there are no large free spaces, Diskeeper has to make them. 200MB of free space is adequate on a 1GB partition (20%), but insufficient on a 4GB partition (only 5%). This is because the larger partition has four times as much room for the free space to be scattered over, so the smaller partition is likely to have larger contiguous free spaces. If you are short of free space, do some housekeeping; clean out old files and garbage files, and archive anything you don't really need on the disk.
Files that are open for exclusive access, including the paging file, cannot be moved or defragmented by Diskeeper. This can be a problem, because the fragments of these files, being immovable, can prevent Diskeeper from consolidating enough free space to defragment the entire partition. You can get around most of this by selecting a time when you can have exclusive use of the system, then arrange that no applications start automatically on booting. In Control Panel/Services, find any applications that start as services and disable them, first noting their existing settings so that you can restore them later. Then set the paging file, if any, on the partition to zero size, both initial and maximum. Now reboot and immediately run Diskeeper in the manual mode. As soon as it has finished, restore the original paging file values and the Services settings, and reboot.
Directory files can also interfere with defragmenting, since they cannot be moved while Windows NT is running. However, Diskeeper 3.0 and later can defragment and consolidate directory files at boot time.
If you can get the "Average number of fragments per file" value down around 1.02, it probably won't matter if there are a few files that are still fragmented. The impact on performance will not be noticeable. Also, having a small number of fragments in a very large file does not make much difference. If, for example, a 10MB file has five fragments, then each fragment averages 2MB; that amount of data takes a relatively long time to read, and the added time from reading an extra fragment becomes insignificant.
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