Hi All,

I just completed running a Robocopy of several 10s of GBs.  Here is my point of confusion, Robocopy completed successfully and in the Totals summary it states that 67.4 GBs were transferred.  At the new location I can verify, by right clicking on the folder and selecting properties that indeed 67.4 GBs were copied.  However, what makes me doubt my confidence is that when I right click on the source folder and select properties it tells me it has 61.8GBs of data.  The destination folder was an empty newly created folder.   Why the discrepancy??

Same OSs, same NTFS cluster sizes?

The source OS is server 2003 Standard and the destination is server 2008R2 SP1 Standard. Both are NTFS but different sizes, the source is 688GB and destination is about 4TBs.

The default NTFS cluster size is the same (4k) but you can check the size on your 2008 R2, here's an example:

C:\WINDOWS\system32>fsutil fsinfo ntfsinfo e:
NTFS Volume Serial Number :       0x002ce67a2ce66a5c
NTFS Version   :                  3.1
LFS Version    :                  1.1
Number Sectors :                  0x00000000747045ae
Total Clusters :                  0x000000000e8e08b5
Free Clusters  :                  0x00000000070df3a7
Total Reserved :                  0x0000000000002c10
Bytes Per Sector  :               512
Bytes Per Physical Sector :       512
Bytes Per Cluster :               4096
Bytes Per FileRecord Segment    : 1024
Clusters Per FileRecord Segment : 0
Mft Valid Data Length :           0x0000000000e40000
Mft Start Lcn  :                  0x00000000000c0000
Mft2 Start Lcn :                  0x0000000000000002
Mft Zone Start :                  0x00000000000c0e40
Mft Zone End   :                  0x00000000000cc820
Resource Manager Identifier :     F5D1332E-B6FB-11E1-B22D-005056C00008

the command is fsutil fsinfo ntfsinfo <your volume>

The cluster size represents the minimum unit you can allocate on the hard drive, so if the cluster size is 4k a file which is 1 byte in size will take 4k to be stored, 8k if the cluster size is 8k

Although aperelli's information is correct, this will only apply if you are looking at the "Size on disk" field in Properties, not the "Size" field.

The "Size" should be the same, but you can enable hidden files, and unhide system files to compare and see if there is other hidden files in the destination directory (Just because it is new and 'empty' doesn't actually mean it is empty) Can't see how these would take up an additional 6GB though.

If looking at the "Size on disk" then aperelli's suspicions are correct, the cluster size is different.

As each file is stored to the hard disk, the next file stored will start at the next sector. As such, the "SoD" will always be larger than the size of the data. Also, if the free space on the destination drive is fragmented (As files get deleted, it creates free space gaps within existing data that will always get used up first, fragmenting new files that get put in these gaps) then each of the resulting file fragments will also round up to the next sector, further increasing the resulting "SoD". Defrag will recombine all the file fragments into a contiguous space on the disk, reducing the "SoD" accordingly.