Avoiding Disk Space Waste

by Mitch Tulloch [Published on 17 May 2006 / Last Updated on 17 May 2006]

How to avoid wasting space on NTFS volumes by modifying the default cluster size.

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:

chkdsk d:

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.

Mitch Tulloch
MVP Windows Server



The Author — Mitch Tulloch

Mitch Tulloch is a widely recognized expert on Windows administration, networking, and security. He has been repeatedly awarded Most Valuable Professional (MVP) status by Microsoft for his outstanding contributions in supporting users who deploy and use Microsoft platforms, products and solutions. Mitch has published over two hundred articles on different IT websites and magazines, and he has written or contributed to almost two dozen books and is lead author for the Windows 7 Resource Kit from Microsoft Press. For more information, see www.mtit.com .

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