Copy of drive - why do size vary?

[JohnDoe2]

Hello

I have a USB flashdisc which is my drive J:

I just tried to copy to an external drive, since I want to reformat J:

Now; before copying, I got the following information when I chose "Properties" on J:

Used Space: 656 572 416 byte

Free Space: 366 952 448 byte

Capacity: 1 023 524 864 byte

The copy procedure went ok. No errors.

When I choose "Properties" on the J: folder on the external drive after copying, I get the following numbers:

NB! Please note: I do not know how to translate the text accurately, but the number given to me are:

567 592 343 bytes

585 469 925 bytes

7856 files, 359 folders

Why such a large difference in bytes from source to destination? Have files been lost?

[schloss]

The two sets of numbers are not the same thing.

Windows allocates space in blocks, not in single bytes: each block is usually (but not always) 4096 bytes. On a flash drive, or external drive with FAT/FAT32 formatting it may be much bigger (4096, 8192, 16384...). So the "allocated" size for a 1-byte file will be actually 4,096 bytes or more.

The first three sizes are "allocated" sizes. The second pair of sizes are the actual file sizes added together.

[JohnDoe2]

The two sets of numbers are not the same thing.

Windows allocates space in blocks, not in single bytes: each block is usually (but not always) 4096 bytes. On a flash drive, or external drive with FAT/FAT32 formatting it may be much bigger (4096, 8192, 16384...). So the "allocated" size for a 1-byte file will be actually 4,096 bytes or more.

The first three sizes are "allocated" sizes. The second pair of sizes are the actual file sizes added together.

Thank you.

Ok; so - bottomline - as long as I got no errors when copying there is nothing to worry about?

[CharlotteTheHarlot]

The two sets of numbers are not the same thing.

Windows allocates space in blocks, not in single bytes: each block is usually (but not always) 4096 bytes. On a flash drive, or external drive with FAT/FAT32 formatting it may be much bigger (4096, 8192, 16384...). So the "allocated" size for a 1-byte file will be actually 4,096 bytes or more.

The first three sizes are "allocated" sizes. The second pair of sizes are the actual file sizes added together.

Thank you.

Ok; so - bottomline - as long as I got no errors when copying there is nothing to worry about?

If you want to be 100% sure you copied all the data you should compare the source and target folders (Windiff, Examdiff, etc). However, if that is impossible because of many gigabytes, then check the source and target properties and make sure both the quantity of Files and quantity of Folders exactly match (not 100% proof of course, but pretty good).

It is less likely but entirely possible that there are NTFS file permissions set or really stringent 3rd party security utilities running that effectively block casual file copying. Totalling up the number of Files and Folders before/after would show that something of this nature is in play, even if your file manager/copier/application fails to show an error.

As JohnDoe2 mentioned, bytes (or more specifically disk spaced used) cannot be compared across dissimilar allocation systems. Even though practically every disk partition starts with sectors that are exactly 512 bytes in size, the formatted file system on a storage device from a Windows OS sets the minimum allocation unit (cluster size) to contain some multiple of sectors. Just considering the Fat16 / Fat32 / NTFS universe, a given cluster may contain an amount of sectors equal to 1, 2, 4, 8, 16, 32, 64, 128, 256, 512 (depending on the OS and total amount of sectors). That translates to anything from 512 bytes to 256 KB minimum allocation unit (albeit some of those are uncommon).

So, any given file of exactly x bytes will actually be a different size on disk for each of those ten possible file systems (with an increasing corresponding amount of slack space disk waste as well). But to make a long story short, if your source and target destinations are not using identical cluster sizes, file sizes in bytes become absolutely meaningless.