On all Qsan Q500 series and AegisSAN LX series products, the SSD cache feature is enabled by default. However the feature is controller by license, you'll need a license file to activate the feature. Please consult our sale team for further details about the license purchase.
After obtaining the license file, simply choose to install the license file from the Web UI, in the maintenance page -> Upgrade -> SSD caching license, followed by a reboot of the system to fully activate the license.
No, once configured on creation, the property cannot be modified. You will have to re-create the RG if you wish to change the thin-provision settings.
A thin-provisioned RG can contain up to 32 RAID sets, the maximum size of a single RAID set in the RG is also limited to 64TB.
The total capacity of VDs created in a thin-provisioned RG is limited to 128TB maximum.
Yes the performance of a thin-provisioned RG is slightly lower than a normal RG.
A VD created in a thin-provisioned RG does not be initialized. Only the data 
By using Thin-provisioning, you're allowed to pre-allocate capacity that is larger than the exisiting RAID disks on the system.
This is also the dependency between the snapshots of the same virtual disk on a system.
This is the dependency between the snapshots of the same virtual disk on a system. When you delete any snapshots for a VD, all older snapshots are automatically deleted. Since without the snapshot you delete, the recored accumulated changes is not complete enough for rolling back to any older snapshot status, and therefore the system automatically deletes the older snapshots by design.  
The write performance of a snapshot enabled virutual disk will be dramatically impacted compared to it's original status without snapshot enabled. The snapshot works on a copy-on-write technology so that when you make changes to a snapshot-enabled VD, it takes additional time to read and write the original blocks to the snapshots space before replacing the contents in the block. And therefore the write performance can be expected to be reduced to less than 50%. As for the read performance it's not much impacted, depends on the overall system loading when the data is read out from the system.