"size" vs "size on disk"?

[JoostVisser]

Hi all,

 

I have this folder on my NAS that I want to copy to my local machine so that I can easily sort the files with a script. But the properties panel reports a "size" and a "size on disk". What's the difference between these and which one should I worry about? 144GB definitely fits on my local drive but 11.4TB definitely doesn't.

 

 

Thanks a lot!

 

[RONOTHAN##]

Almost every NAS I know of has compression turned on by default, so the size on disk is what the files become after being compressed.

 

But I'm just realizing that I misread that as "11.4 GB" instead of TB, so there's almost certainly something wrong there. 

 

EDIT: I've got an idea why this is happening, does your NAS happen to have snapshots turned on, and do you do a lot of modifications to the files in the folder?

Edited October 18, 2021 by RONOTHAN##

[HanZie82]

I wanted to explain everything myself in my generally lacking translatory skills, but this page has all the info i wanted to say and more...

https://askanydifference.com/difference-between-size-and-size-on-disk/

[Eigenvektor]

Size is the actual size of the file.

 

Size on disk is the amount of space it occupies on the disk. This is based on the disk's cluster size.

 

For example if you have a cluster size of 4KB, then a 1 byte file will occupy at least 4KB, because that's the smallest logical unit your drive can address.

 

The huge differrence makes me suspect the drive was optimized for large file, i.e. uses a large cluster size but actually contains a large number of tiny files.

[porina]

Depending on the file system, files can take a minimum size which inflates the used space over the actual file size total. However, that doesn't account for it exceeding physical storage.

 

One possible reason for that might be if you have links to files or folders somewhere in there. Again, depends on the filesystem used. You could have the same file referenced multiple times for example.

 

Another possible reason is that you can have multiple streams per file. It is possible some file(s) might have an absurdly large allocation for that alternate stream somehow.

[JoostVisser]

So many replies I can barely keep up! Thank you!

 

from what I'm gathering here is that the difference has mostly to do with the file system. So I'm going to go ahead and assume that when I move the files to my local machine, the size on disk value will be a lot closer to the size value. 

@Eigenvektor I tested it with a .txt file and found that the cluster size is 256MB I think. I made a .txt of 12 bytes and it had a size on disk of 256MB

 

@HanZie82 thank you! Definitely a helpful article

 

@RONOTHAN## I have no idea if the NAS has snapshots turned on, but if it does that would be a very good explanation

 

@porina if a file is referenced, say 3 times does it really take 3 times the storage on disk? Not entirely sure what you mean by streams, can you elaborate?

[porina]

2 minutes ago, JoostVisser said:

@porina if a file is referenced, say 3 times does it really take 3 times the storage on disk? Not entirely sure what you mean by streams, can you elaborate?

I don't know how smart or stupid file explorer is, but there is some risk it might count multiple times.

[Kilrah]

I don't think it's even possible to have 256MB clusters, it's likely the NAS share reporting some bogus values, in this case I'd just ignore the "size on disk".

[JoostVisser]

On 10/19/2021 at 10:19 AM, Kilrah said:

I don't think it's even possible to have 256MB clusters, it's likely the NAS share reporting some bogus values, in this case I'd just ignore the "size on disk".

I copied the folder to my local machine and both size and size on disk are ~144GB, with a delta of ~100MB so that's all good!