Challenge
In some cases, depending on infrastructure setup you can observe poor processing rate when performing full VM restore in SAN mode. You can notice as well that Network mode is faster.
Cause
If you restore Thick Lazy Zero disk using SAN mode, overall restore performance can be affected because of round trips through the disk manager APIs, AllocateBlock and ClearLazyZero requests. The reason that NBD mode can work faster in comparison to SAN mode (when not using block-sized writes) is because the write is performed by the host which has inside knowledge about layout of the vmdk. This inside knowledge must be requested from the host when VDDK is doing direct writes to the LUN.
Solution
Use alternative transport mode: network, virtual appliance
You can also try to restore in SAN mode via standalone ESXi. In some cases you may see a higher processing rate
More information at kb.vmware.com/kb/1035096