HyperBack backs up used blocks

Summary

When HyperBack backs up virtual machines, the process may take longer despite small used space. This is because HyperBack backs up used blocks on the virtual HDD, which isn't a bug. The used blocks can be reduced with [Dynamic] or [Thin] provisioning, depending on the hypervisor.  

Hyper-V (Dynamic):  Used blocks can shrink, but the VHDX size won't reduce.  
ESXi (Thin):  VMDK size can shrink, but the used blocks can't be reduced.

Different hypervisors handle block reduction differently.

 Details

- Hyper-V

Windows：For Windows with [Dynamic] disks, used blocks are automatically reduced when data is deleted, but the VHDX size stays the same.  
Linux：For Linux with [Dynamic] disks, deleting data doesn't reduce used blocks automatically. You can use the fstrim command to reduce used blocks, but the VHDX size remains unchanged. 

Method	Windows	Linux
Dynamically expanding	The used blocks are automatically reduced when the data are deleted	Data deletion does not automatically reduce used blocks. *The use of fstrim command can reduce used blocks
Fixed size	Disk Size = Used Blocks	Disk Size = Used Blocks

- ESXi

Windows：For Windows with [Thin] disks, when data is deleted, the actual used space matches the VMDK size, but the used blocks remain at the expanded size.
Linux：For Linux with [Thin] disks, deleting data doesn't automatically reduce used blocks or VMDK size. Using the fstrim command can make the actual used blocks roughly equal to the used blocks and VMDK size. 

Method	Windows	Linux
Thin	Data deletion does not automatically reduce used blocks *Resetting CBT only can reduce the used blocks.	Data deletion does not automatically reduce the used blocks *The use of fstrim command can reduce the used blocks.
Thick(lazy)	Data deletion cannot automatically reduce the used blocks	Data deletion cannot automatically reduce the used blocks
Thick (eager)	Disk Size = Used Blocks	Disk Size = Used Blocks

• The behaviors mentioned apply when there are no VM checkpoints or snapshots; otherwise, they may differ.
• For instructions on resetting CBT, please visit here.
• To make "Virtual HDD size" match "actual used blocks," use these commands
  • Windows：defrag <Drive Letter：> /U
  • Linux：fstrim –v <mountpoint>
• If "not support" appears after running the fstrim command, edit "fstab" to "default,discard" and restart the OS.

Target Products

- ActiveImage Protector 2018 / 2022

(36591935314201)