Yes, the system will do the full copy upon first time execution of the task. Afterwards the replication will be carried out in incremental manner.
The replication feature basically works on snapshot bases, every time a replicatoin task is executed, a snapshot is taken on the source zfs and then sent to the destination zfs. The zfs replication mechanism automatically checks and compares the snapshot versions between the source and destination to make sure the snapshots are identical and via comparison between the snpashots, decides which incremental data needs to be sent.

On Qsan NAS only blocks with data need to be rebuild upon any disk replacement. The more data you have in the pool, the longer it takes to rebuild. Besides, try to avoid frequent user accesses to the storage during reb uilding process as the more I/O interference during rebuilding (from running data services), the slower the rebuilding speed could be.

No, for using the replication feature you don't need a license to activate it. The feature is directly configurable in the Web UI -> Service configuration > Backup > Replication.

You can create up to 16 tasks for all Qsan NAS models except only 8 for U1 series.

No, it's file level feature. So if the task fail please try to do the task again.

Yes, if the Rsync job had been ever stopped, just restart the job, and then it will verify the backup file with two sites. The file that didn't backup will continue to Rsync process.

All Qsan NAS with 12 bays or more have full support to SSD cache feature.

Considering system stability, we would only recommend SSD disk models listed in the compatibility matrix to be used. However, any unapproved SSD cache drives could also be used in this case as long as they can be detected and recongnized by the system. As the contents stored on SSD cache drives are only cached data, the original dataset would not be impacted upon any SSD cache drive mulfunction events, though performance would then be dropped down to the status without SSD cache drives in the worst case.

The Qsan NAS products support up to 6 SSD cache drives (4 read and 2 write) for every pool created in the system.