Add parameter to control UNMAP granularity / provisioning slab for Windows...

Hello,
I’m using SCST with vdisk_fileio and Windows (iSCSI initiator).
Thin provisioning and UNMAP work, but Windows reports the following error during defrag /L (ReTrim):
“The slab size is too small”
Windows INBOX iSCSI initiator requires the storage to report provisioning slab ≥ 4096 bytes via VPD pages (LBPRZ/LBPPBE/OPTIMAL UNMAP GRANULARITY).
Currently, SCST only exposes lb_per_pb_exp, which affects LBPPBE, but there is no parameter to set the provisioning slab (also UNMAP granularity).
As a result, Windows sees:
Logical sector: 512
Physical sector: 4096
But slab = 512 (too small → ReTrim fails)
Could you please add a configurable parameter for:
Provisioning slab size (e.g. unmap_granularity or slab_size)
Optionally, UNMAP alignment
These values must be exposed via the appropriate VPD pages so the Windows initiator will accept the device for ReTrim/Optimize.
This would greatly improve Windows compatibility for thin-file-backed LUNs (vdisk_fileio), especially in virtualized storage setups.