If you’ve ever formatted a hard drive or USB stick, you may have noticed the “Allocation Unit Size” setting. It is entered by default, but can also be changed. But should you? And if so, what would be the correct value? What does “assignment unit” actually mean?
This role is played by the allocation unit for your storage
There are several answers to the above questions, both simple and not-so-simple. Since SSDs are now becoming the standard drive type in many systems, the negative effects of allocation units that are too small are weakened somewhat, while on the other hand the advantages of larger allocation units (or clusters) can increase.
Depending on who you are speaking to, the allocation unit size can also be referred to as the “cluster size”. This is the size of the smallest possible block of data on your drive.
Basically, even a completely empty file will be as large as the assigned allocation unit. This means that every single file on your drive will be at least that big. This can potentially take up a lot of space on your hard drive if you are storing a lot of small files but have a large allocation unit set. To use an extreme example, if you set an allocation unit of 1MB and you store ten files that are 8KB each, each of those files would also take up 1MB, so the total used space would be 10MB instead of 80KB. This is a lot of wasted space!
The allocation units on the hard disk determine how much space individual files take up on the drive. This is particularly important with a large number of small files, because each file requires an allocation unit.
The Windows 10 default Allocation Unit size is 4096 bytes (4 kilobytes), which is pretty small and probably shouldn’t be a huge waste of space on most computers. However, making the allocation unit size too small can result in a slower system – the allocation will take longer because more allocation units are allocated to each file. However, if you choose too large the size of the allocation unit, valuable storage space is wasted.
The optimal allocation unit size for your drive depends on which operating system you are using and the size of the drive. For example, the Microsoft website has a list of standard sizes for different versions of Windows. We urgently recommend using the standard size of the allocation unit on the drive or partition with your operating system.
However, this may be different on other partitions depending on what you want to use them for. For example, if you have a partition that you use exclusively for movies, a large allocation unit makes sense because a single movie file is typically hundreds of megabytes or even a few gigabytes in size. You could even use the maximum allocation unit size of 2MB – but keep in mind that doing so will make smaller files (like closed caption files) take up at least that amount of space.
Not everyone can relate to the term “allocation units” in hard disks. If in doubt, leave the Windows 10 standard of 4096 bytes.
When you have a drive for movies, pictures, and music, the situation changes because picture and music files are much smaller than movies. In this case, try to keep the size of your allocation unit just below the size of your music and movie files.
However, there are not many scenarios in which it is advisable to set the allocation unit size smaller than the standard size; after all, you will rarely work with files under 1 KB in size. If the allocation unit is set very small, you will only slow down the reading of larger files through your drive. If in doubt, you should leave it at the default setting.
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