# What is 'Allocation Unit Size'?



## jhonrox

Hello there,

This question might sound simple to most of you, but could some one tell me what allocation unit size is, please? I was recently trying to format a harddrive and I am confused as to which option to choose:







Does it matter what I choose? How would it affect the hdd performance? Because I was in doubt, I chose 'default allocation size'.

Thanks in advance!


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## enothor

The allocation size is the cluster size, if you're using the HDD for your primary disk then you'd want to use the larger size for better performance (faster), if you are using the drive for storage, then it would be fine to make it smaller and save more space on the disk for storage, unless you are using the disk to store things like media files such as mp3's and what not, then you'd want to leave it larger still.  Like 4096 is fine, it's about the standard.


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## jhonrox

enothor said:


> The allocation size is the cluster size, if you're using the HDD for your primary disk then you'd want to use the larger size for better performance (faster), if you are using the drive for storage, then it would be fine to make it smaller and save more space on the disk for storage



Thanks a lot for clearing up the confusion, enothor!


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