@florent it was 2 windows vm's, both with 100gb but not even 50% filled. Edit: All Linux VM's worked tho.

@tsukraw There's no need to uninstall the old version, the upgrade is enough. The feature to disable time sync is also just a convenience shortcut for setting the TimeSyncMode value in HKLM\SYSTEM\CurrentControlSet\Services\xenagent to a DWORD of 0. You can set it manually or through Group Policy if you wish. (In fact, GPO might be a better solution on domain environments)

@rizaemet-0 this is not configurable . before qcow2 the S3 blocks were aligned with the VHD blocks, then compressed, so changing it would have been a lot of work now with qcow2 support almost reaching stable, we have some of the tools available to resize the block size on the file ( since qcow2 are based on 64KB blocks) , so it's not impossible, but it's still quite complex to do reliably Could you name the provider ?