Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

How can I calculate the number of free clusters that exist on a freshly formateed NTFS 1.0 TB hard drive?

I began running chkdsk (osn an external USB connected hard drive) about 12 hours ago and it has thus far completed the checking of 1,500,000 free clusters.

Is a cluster simply the allocation unit size? (AKA the smallest possible filesize?)

Because if it's ~4kb and my drive has 1,099,511,627,776 bytes that means there are 268,435,456 total free clusters and my entire chkdsk session will take about 2,150 hours to complete.

Should I just cancel the chkdsk and redo it from a SATA port?

share|improve this question
up vote 2 down vote accepted

Yes, clusters and allocation unit size are normally the same. Files are split up into logical chunks on the disk based on the allocation size.

4KB is the default on some systems, but I thought that Windows would automatically increase the cluster size depending on how big your drive is.

You might enjoy for further information and diagnosing the problem yourself (i.e. to detect your ACTUAL allocation size).

P.S. -- USB 2.0 is a terrible protocol for a hard disk, so I would strongly recommend that you find any other alternative possible and use that instead. Especially with such a huge disk... 1 TB is a lot.

If you're doing a "full" chkdsk to make sure that the system can reliably read and write from every sector, it's going to take many hours regardless of which link you're using, though. If there is actually a bad sector on the disk, don't worry about it (unless there are many); the filesystem will automatically handle it when it gets a write error.

share|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.