Avoiding Disk Space Waste
If the default cluster size for an NTFS volume is set too high, the result can be wasted disk space. For example, to determine your default cluster size for D: drive, type the following:
The line in the result where it says "...bytes in each allocation unit" gives you the current default cluster size for the volume, which is usually 4096 bytes (4 kB). To determine whether this is optimal, open My Computer, double-click on D: drive, use Edit | Select All, and use File | Properties. On the properties sheet that is displayed, compare Size with Size On Disk. If they're pretty close to each other (say around 10%) then you're probably using the best cluster size for your volume, but if Size is significantly greater than Size On Disk, then you could consider giving the volume a smaller cluster size. To modify the cluster size you must reformat the volume, so back it up first and then type this command:
format d: /a:2048
This will reformat D: drive using 2 kB clusters.
MVP Windows Server