If you’ve ever formatted a hard drive or USB flash drive, you may have seen the “Allocation Unit Size” setting. This is set by default, but you can change it if you want. Should you? If so, what should you pay it to? What does the size of the allocation unit mean?
There are several answers to the above questions, both simple and not so simple. With SSDs becoming largely the default drive type on many systems, the negative impact of having allocation unit sizes that are too small is somewhat diminished, while on the other hand, the advantages of the sizes larger allocation unit (or cluster) may increase.
What does the size of the allocation unit mean?
Depending on who you are talking to, the size of the allocation unit may also be referred to as the “cluster size”. Either way, it’s pretty straightforward. This is the smallest piece of data possible on your drive.
Basically even a completely empty file will be the size of your allocation unit. This means that every file on your disk will be at least this large size, potentially taking up a lot of space on your hard drive if you have many small files but a large allocation size.
To use an extreme example, if you have ten 8KB files but an allocation unit size of 1MB, each of those files will actually occupy 1MB, so the total amount of disk space used would be 10MB. and not 80 KB. That’s a lot of wasted space!
The default Windows allocation unit size is 4096 bytes (4 kilobytes), which is quite small, and on most computers this is unlikely to waste much space.
If you reduce the size of your allocation unit, it may result in a slower system – allocation will take longer because there will be more allocation units assigned to each file. If you increase the size of your allocation unit, it will take up valuable disk space.
What size allocation unit should you use?
The optimum allocation unit size for your disk will often depend on the operating system you are using and the size of the disk. For example, Microsoft has a list of default sizes for different versions of Windows available on its website.
On your operating system drive or partition, we strongly recommend that you use the default allocation unit size. But on different partitions this can change depending on how you use it.
If, for example, you have a partition or drive that you use exclusively for movies, then it makes sense to use a large allocation unit size, as a single movie file tends to be several hundred MB, or even a few GB. So you can use the maximum allocation unit size of 2 MB, but keep in mind that smaller files (like subtitle files) will use this amount of space at a minimum. space.
If you have a dedicated player for movies, pictures, and music, that makes a difference as picture and music files are much smaller than movies. Try to make the size of your allocation unit just below the size of your music and movie files.
There are not many scenarios in which it is recommended to reduce the size of the allocation unit from the default. There are few modern scenarios in which you will be working with files smaller than 1KB, and you will simply slow down your drive’s reading of larger files.
So, when setting the allocation unit size, always analyze the given drive or partition and determine what is best for it. If in doubt, leave the default.
Should you use different sizes for SSDs or hard drives?
As mentioned above, fragmentation does not present the same issues on an SSD as it does on a hard drive. For this reason, you can theoretically use larger allocation unit sizes without affecting performance. Would that really speed things up?
The answer is probably no. So far, there have been no real-life examples of larger allocation unit sizes leading to performance changes on SSDs, although theoretically this could be the case due to the lower complexity. your file system and faster read-write speeds.
If you’re worried about using up your SSD early, that won’t have much to do with it. Instead, see our guide on checking the health of your hard drive in Windows 10. Also see our guide on the difference between a DRAM SSD and a DRAM-free SSD.
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