Free disk space issue

Dear Jim,

Thank you for posting your question on our forum.

There are several reasons for the discrepancy in free space between two external hard drives with the same amount of data:

• File System Overhead: The file system itself takes up some space. This includes the master file table (MFT), file descriptors, and other metadata that the system uses to manage files.

• Cluster Size: Drives are divided into clusters, which are the smallest units of storage. If the cluster size is different on each drive, there can be more wasted space (slack space) on one drive than the other, especially if there are many small files.

• Hidden/System Files: There might be hidden or system files that are not accounted for when you look at the visible data. This includes files like pagefile.sys, hiberfil.sys, or system restore points.

• Drive Formatting: Even if two drives are advertised as the same size, the actual usable space after formatting can differ slightly due to rounding differences in the way the drive's capacity is calculated.

To investigate further, you may use disk analysis tools to get a detailed breakdown of the space usage on each drive. Tools like WinDirStat or TreeSize can help you visualize where the space is going and identify any hidden files that might be taking up space. Additionally, checking the cluster size and reformatting the drives with the same cluster size could help align the free space more closely if necessary. Remember to back up all data before attempting any reformatting.

Should you have any other questions or need further assistance, please do not hesitate to contact us.

They exactly the same 2 HDs, same manufacture, same formatting, same info stored within, cloned basically. I used to be in IT for a very long time so I get what you wrote technically but nonetheless, logically it makes no sense. I will check out the tools you pointed out.

I installed WinDirStat and studied it closely. All I accomplished was to open the door to more questions. There is a category on the folder structure call "unknown". The difference between the 2 HDs is 50MB. I supposed when you consider that the drives are 3.63TB it's not that much but that's not the point to the effort. I wanted to let you know what came of this. None of what you wrote above as far possibilities seems applicable... just saying.

Let me change from my last post. You can turn on "Unknown" under the options pulldown. One HD is 203.2 GB and the other 281.7 GB. That's pretty significant difference. I likely will never know what this is all about, what's going on here.

Dear Jim,

Thank you for your reply.

Please take into consideration the following factors as well:

1. File system corruption. Running the chkdsk command might find file fragments that could occupy space

2. Sparse files, compressed files, and junctions. If these are not handled correctly during copying, it may lead to differences in space usage

To ensure both drives have exactly the same information and to potentially resolve the free space issue, you could use a file synchronization tool like Microsoft's SyncToy, or use the ROBOCOPY command with the /MIR switch to mirror one drive to the other. This can help identify any discrepancies in the data that might be causing the difference in reported free space.

Please let us know if this helps.

Thank you.

I've used ROBOCOPY on file servers years ago, I am familiar. To be clear, this is just pissing me off more than it creates an actual problem for me from a practical perspective. It's like one of those "in theory" sort of things that there is no reason for there to be such a big change. A 52GB difference is not a small thing, not to mention what is going on with the other "unknown" 200GB within itself. You refer to "chkdsk" which has been around forever. I would that some of the functions built into "BoostSpeed 13" to be at least as effective as the Disk Doctor for example. I have also used the check disk sort of thing that comes up under Properties when you right click on a folder and select Tools. Back to the point of all of this... you can tell me that there isn't anything built into BoostSpeed 13 to help with this? I look forward to a reply and am advising that this is the last email I will send on this topic as to not beat the issue to death. Thanks ~ Jim

Dear Jim,

Thank you for your reply.

If you are absolutely sure that both disks are identically partitioned (have the same partition table), you can try locating occupied space by comparing the sizes of both disks’ catalogs in DiskExplorer.

If your disks are partitioned to NTFS, one of the disks may have its MFT table significantly grown, thus decreasing free space with no obvious reason. You can trace this by checking the cluster map in Auslogics Disk Defrag (MFT is usually marked violet). Or you can visually compare the cluster maps for both disks.

In case you decide to dig deeper and would like our assistance with that, please send us some additional information:

- screenshots showing the cluster maps for each disk;

- your system information logs (Start => Run, type in MSINFO32 => Enter. Save the report using the File => Save menu option);

- Disk Management window screenshot with the size tables visible in it (please see an example below):

- screenshot showing the page where you are checking the disks’ sizes.

Thank you.