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Why is size on disk a different (larger) size then "size" itself, please see attachment

Posted on 2016-09-29
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Why is size on disk a different (larger) size then "size" itself, please see attachment

I have copied a NAS fully from an old NAS to a new NAS, one on one, no errors. As you can see, the "size" is virtually the same on old and new.

Left side is old (source) and right side is new (target)
Right side is a bit larger since people already put new files on it.

Language is Dutch, so:

grootte = size
grootte op schijf = size on disk
bestanden = files
mappen = folders

I would expect all to be the exact same size and count.
Data size
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Question by:Agrippa
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by:Qlemo
Qlemo earned 1000 total points
ID: 41822703
Looks like either the old NAS size count is bogus, or cluster size is laaaarge (leading to an average of 1 MB overhead per file?!), The physical storage space is a matter of the file system and its parameters; the important part for comparison is "Grootte", at least as long as it is less than the  size on disk.

How did you perform the copy? Are both file systems the same type?
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by:Agrippa
ID: 41822705
Hi Qlemo,

the copy was through a PC, just using Windows Explorer. I also did it once with rsync, but when I saw the size difference I thought: let's see what Explorer makes of it. Same outcome.

File systems are as far as I know the same
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by:Joe Winograd, EE MVE 2015&2016
ID: 41822717
> I've used the "embed" feature for images in your question, to display them inline.

I'm not addressing the question, but want to voice my agreement with Qlemo on the value of embedding images inline in posts. If you're not familiar with the method, these two EE articles will help:
How To Embed Screenshots in Posts
How to Embed Screenshots and Other Files with My Personal Knowledgebase

Regards, Joe
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by:Agrippa
ID: 41822731
Thank you Joe
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Mal Osborne earned 1000 total points
ID: 41822801
Yep, data is stored on a filing system in "Clusters". A single cluster is (often), the smallest amount of space that can be allocated. Cluster size is dependant on the OS, type of file system, and options chosen during formatting.

If you have, for instance, a 2Gb USB key, formatted as  FAT16, the cluster size will be 64Kb. Thus, a 1Kb or 2Kb or 10byte of 63Kb file will use one cluster, occupying 64K of space. A 65K file will use 128Kb of disk space.  1000 500byte text files will have a total file size of 500Kb, but use 64000Kb of disk space. The wasted space is termed "slack space".

In general, smaller cluster sizes means more efficient storage of small files, but more overheads and disk space used to track the larger number of clusters.

NTFS addresses this problem to some extend by allowing small files to be stored in a structure called the MFT, or Master File Table. NTFS also allows a larger number of smaller clusters, and has a more efficient index.

In your case, it seems you have copied a large number of small files, from a drive with large clusters, to one with small clusters.
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