1. The user private data will be stored in the userhome pool as user's exclusive folder. 
2. The user quota is applied for the user's folder capacity in the UserHome.
No, the user quota only can be used in the UserHome. The user quota is applied for the user's folder capacity in the UserHome. 
U1/U2/U3 series has built-in antivirus service provided by McAfee, while U4/U6 series supports iCAP based AntiVirus server,which has to be configured separately and works externally to the U4/U6 units.
You may enable the service via WebUI as the follows, configuration > Service configuration > Antivirus.
After the antivirus service is enabled, you may also  create scheduled tasks for regular scanning.
No, the antivirus services only works for file level data, not for block level volume data
For NAS units with built-in antivirus services, we provide 3 years license. If the license expires you may contact Qsan or the antivirus service provider to renew the license.
Using antivirus service on Qsan NAS will certainly occupy some system resources and cause some reduction on system performance. Level of impact depends on the file size and amounts scanned in a fixed period of time, the more files to be scanned, the heavier the loading is the thus impact on system performance is bigger.
The replication feature allows you to copy one entire zfs from a source pool to a destination pool in either local or remote manner. For running a replication task successfully, sufficient space on the target pool for the task to create a replica zfs is required. For any issues encountered during setting up a replication task, please contact Qsan support for further details.
Yes, zfs replication replicates all properties from the source zfs to the target zfs, including all the options you see while creating the source zfs.
The replication feature works at block level, and is SSH encrypted.