Why is size on disk different on a flash drive when I copy a large amount of files?

Hi EverydayAden,

Yes, please don't worry, the difference in disk size does not affect the actual files themselves.

In addition, while the size difference on the disk is mainly due to the operating system and its associated files, it should not impact the actual files or data stored on your system. However, it's always a good practice to regularly back up your important data to ensure it remains safe during any system changes or upgrades.

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Please feel free to post back if you need further assistance.

Hello EverydayAden,

Thank you for using Microsoft products and posting to the community.

The difference in the "size on disk" between your internal SSD and a flash drive (formatted in NTFS) when copying files can be explained by differences in cluster size and file system overhead. Here's why this occurs:

1. Cluster Size: A file system, such as NTFS, divides storage space into clusters or allocation units. The cluster size is the smallest amount of disk space that can be allocated to a file. Smaller files can result in a portion of a cluster being unused, leading to "slack space" or "wasted space."
2. File System Overhead: File systems have metadata structures, such as the Master File Table (MFT) in NTFS, that store information about each file and directory. This metadata takes up space on the storage device and contributes to the "size on disk."
3. Fragmentation: Fragmentation can occur over time as files are created, modified, and deleted. Fragmented files may occupy non-contiguous clusters, which can increase the "size on disk" for those files.
4. NTFS format features: Writing a file to an NTFS partition keeps a copy of the file in memory. But there is a difference when you copy a file to a flash drive retaining only a record of the last modification.

In summary, the "size on disk" discrepancy is mainly due to how different storage devices handle file allocation, metadata storage, and cluster size. It's a normal variation between storage mediums and file systems. If you want to minimize this difference, you can try formatting your flash drive with a smaller cluster size, but keep in mind that smaller cluster sizes can be less efficient for larger files. Additionally, compression settings and the presence of fragmented files can also contribute to differences in "size on disk."

I hope the above information is helpful. Please feel free to post back if you need further assistance. 

Sincerely

Mavis - MSFT | Microsoft Community Support Specialist

I fully understand your feelings of concern. If you have any questions in the future, you could post threads in the community, and we will be more than happy to support you.

We appreciate your feedback, please click Yes or No to help us improve the support experience. 

Hope you are keeping safe and well.

Hello EverydayAden,

Thank you for using Microsoft products and posting to the community.

The difference in the "size on disk" between your internal SSD and a flash drive (formatted in NTFS) when copying files can be explained by differences in cluster size and file system overhead. Here's why this occurs:

1. Cluster Size: A file system, such as NTFS, divides storage space into clusters or allocation units. The cluster size is the smallest amount of disk space that can be allocated to a file. Smaller files can result in a portion of a cluster being unused, leading to "slack space" or "wasted space."
2. File System Overhead: File systems have metadata structures, such as the Master File Table (MFT) in NTFS, that store information about each file and directory. This metadata takes up space on the storage device and contributes to the "size on disk."
3. Fragmentation: Fragmentation can occur over time as files are created, modified, and deleted. Fragmented files may occupy non-contiguous clusters, which can increase the "size on disk" for those files.
4. NTFS format features: Writing a file to an NTFS partition keeps a copy of the file in memory. But there is a difference when you copy a file to a flash drive retaining only a record of the last modification.

In summary, the "size on disk" discrepancy is mainly due to how different storage devices handle file allocation, metadata storage, and cluster size. It's a normal variation between storage mediums and file systems. If you want to minimize this difference, you can try formatting your flash drive with a smaller cluster size, but keep in mind that smaller cluster sizes can be less efficient for larger files. Additionally, compression settings and the presence of fragmented files can also contribute to differences in "size on disk."

I hope the above information is helpful. Please feel free to post back if you need further assistance. 

Sincerely

Mavis - MSFT | Microsoft Community Support Specialist

Thank you so much for explaining all of this so simply and easily! So this difference in size on Disk won’t effect the actual files themselves, right? I’m looking to transfer a lot of stuff to a high capacity flash drive or external SSD so I can use my internal one for other stuff like more games, and I was worried about slight differences in files somehow.

Hi EverydayAden,

Yes, please don't worry, the difference in disk size does not affect the actual files themselves.

In addition, while the size difference on the disk is mainly due to the operating system and its associated files, it should not impact the actual files or data stored on your system. However, it's always a good practice to regularly back up your important data to ensure it remains safe during any system changes or upgrades.

We appreciate your feedback, please click Yes or No to help us improve the support experience. 

Please feel free to post back if you need further assistance. 

Thank you! I unnecessarily worry a lot when it comes to computers but this is great peace of mind. I really appreciate it