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Which Allocation Size Should You Use When Formatting A Hard Drive?

When going to format a hard drive in Windows, the default file allocation unit size is 4096 bytes, however there are a whole bunch of other choices to pick from:


Is there a speed difference?

Yes. Selecting a larger cluster size results in faster access times.

Why is there a speed difference?

Because with larger clusters there are less clusters to record, resulting in less records in the table, resulting in less “work” when retrieving files.

What are the larger cluster sizes best suited for?

Big files, such as ripped DVDs, raw AVI files and things of that sort.

Conversely, if most of what you store is smaller files, the smaller cluster size is more suitable.

Does cluster size affect overall space available?

Yes it does.

A quick example using a 4GB USB stick:

Formatted using 1024 byte cluster

Formatted using 4096 byte cluster

Formatted using 32k file cluster

What if I don’t know which to choose?

This is why the default cluster size is 4096 bytes. If unsure, use 4096.

How can I find out what the current cluster size of a hard drive is?

This is done using CHKDSK, as seen above.

1. Launch a Command Prompt. (If using Windows Vista or 7, you must ‘Run As Administrator’).

2. Type CHKDSK (DRIVE LETTER HERE): and press Enter, such as CHKDSK D:

3. The final report at the end of CHKDSK will state the bytes in each allocation unit.


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5 thoughts on “Which Allocation Size Should You Use When Formatting A Hard Drive?”

Cool New Gadgets says:
The bigger the better, looks like I’ve just found the right solution to my problem…
Rick says:
Yes, I’ve noticed these differences from a long time ago when using USB flashdisk, copying, say, the same folder of 100 MB but one contains only 1 file while the other contains 1000 files or more.

1 file was done in seconds while the 1000-more 1 files done in minutes.

James says:
ok so these new 4K sector drives, like the WB EARS 2TB, should be formated with the 4096 cluster size?
willys says:
How do you change cluster size of a hard disk?
Steve says:
Me thinks you assume a lot in the above article. An explanation of the variations shown would be very meaningful to many. i.e. That with larger allocation units you reduce the number of small files you could store. etc. If you assume everyone understood those screens, then they don’t need your service.
Steve Wohl
Rich says:
You’re so right. Nobody knows what “total disk space” means. How silly of me.

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Feb 16, 2011

643 Articles Published