Difference in the occupied space between the Windows client and storage host

The discrepancy between Windows and Open-E JovianDSS storage host in the occupied space on zvol is a result of the lack of support for TRIM on ReFS on iSCSI/SAN disks on Windows Server, which is confirmed by Microsoft and independent documentation (listed below). To avoid this issue, NTFS should be used.

The TRIM/UNMAP mechanism on remote block disks is supported natively since Windows Server 2012, but only in combination with the NTFS file system or as part of Storage Spaces - ReFS in the Windows Server 2016/2019/2022 releases skips these commands.

Links to official and external documentation:
https://learn.microsoft.com/en-us/windows-server/storage/refs/refs-overview
https://www.veeam.com/kb2792#:~:text=,combination%20with%20ReFS%20block%20cloning