External Harddrive - Files take up more space on External than they do on Harddrive

[SPNarwhal]

So I'm partitioning my girlfriend's external, and I took her stuff off just to be safe, but for some reason all of her stuff on the external takes up 223.8gb of space, but when I transfer it to my iMac's harddrive it only takes up 219.81gb.

What gives?

 

[blueroom]

How is it formatted?

 

[SPNarwhal]

Fat32

 

[CylonGlitch]

Fat32

That's why. FAT32 uses a large block size to accommodate the larger hard drives. But in doing so, uses up more space at the end of every file. If the block size is 32kb then even a 1 byte file will use 32kb and all files are rounded to a 32kb size. Now the file system knows where the real end of the file is, but needs to allocate the full 32kb regardless if 1 byte is used, or all 32kb are used.

On nfs, ntfs, hpfs, and other file systems, this problem doesn't exist.

 

[SPNarwhal]

Ah, alright. That makes a lot of sense.

Another question.

When I go into informatiion for the Harddrive it says
219,697,165,912 bytes) for 42,946 items

But when I go into information for it's copy (on my iMac) it says
(219,715,384,432 bytes) for 43,057 items

So why is there more items/files in the copy than there are in the original? And the one with more files is actually smaller.

I just want to make sure I got everything before I partition/wipe her drive, just confused as to why there's more files when it was just a copy of the exact same thing. Hopefully there's another logical answer for this. someone?

 

[jdechko]

On nfs, ntfs, hpfs, and other file systems, this problem doesn't exist.

NTFS defaults to 4k clusters/blocks
HFS+ defaults to 512 byte clusters/blocks

But cluster size is still a possible explanation of the problem at hand.

EDIT: So according to wikipedia, HFS+ uses 512byte blocks, but according to Apple developer documentation, HFS+ uses 4k blocks.

https://secure.wikimedia.org/wikipedia/en/wiki/HFS_Plus
https://developer.apple.com/library/mac/#technotes/tn/tn1150.html

 

[CylonGlitch]

But cluster size is still a possible explanation of the problem at hand.

EDIT: So according to wikipedia, HFS+ uses 512byte blocks, but according to Apple developer documentation, HFS+ uses 4k blocks.

Yeah, the point is that FAT32 does a lousy job of optimizing space.

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So why is there more items/files in the copy than there are in the original? And the one with more files is actually smaller.

I'm guessing what it is counting are the hidden files that the OS makes. Typically the .DS_Store file is one per directory. Could be others, but that one rings a bell.

 

[Ruahrc]

Well that is not entirely true. IIRC you can format a FAT32 drive with 4k clusters, it's just that Windows and OS X do not do so by default. I remember back in the day I could format a FAT32 drive using the windows command line tool and you can specify in the format command to use 4k clusters.

It might be possible to do the same with an HFS+ drive using the terminal- there is probably a verbose command mode that you can use to specify the desired block size.

Ruahrc