Although the larger allocation unit size can help save much time in reading data, it will waste some space. Generally speaking, the smaller allocation unit size on the hard drive can help save storage space better. So, you might wonder what’s the best SSD allocation unit size. When you are formatting an SSD drive, the allocation unit size is set by default based on the partition size. What allocation unit size should you use for SSD? However, if you save a 513-byte file on the partition of 512 byte allocation unit size, it will occupy 1024 (512*2) bytes storage space, which will waste some space (you can do a rough match with the equation: (cluster size)/2 * number of files. If the file sizes do not come out to an even multiple of the cluster size, additional space will be used to hold the file up to the next multiple of the cluster size.įor example, when you store a 512-byte file into a partition with 512-byte allocation unit size, this file will take up 512 byte storage space. This file will be divided into several parts by the allocation unit size and stored on the hard disk. It represents the smallest amount of disk space that can be used to save a file.Įach allocation unit size can only hold one file. All the file systems organize your hard disk based on the allocation unit size/cluster size.

So, what is the allocation unit size? The allocation unit size is also called as cluster size. If you have ever formatted an SSD, HDD, USB thumb drive, SD card or other hard drives, you might have seen the “Allocation Unit Size” setting.

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