create iSCSI traget for BackupExec on QNAP NAS

hi

I'd like to create 55TB iSCSI target on Qnap TS-EC1279U-RP for BackupExec 2010 sp3 and save Windows server over 1GB LAN.
All 4 QNAP ports are already configured as IEEE 802.3ad Trunking and LACP Trunking setuped on 4 ports from HP switch ProCurve, to get best transfer rate.
Should I create "iSCSI Target with a mapped LUN" or "iSCSI Target only"?
If I should create "Target with a mapped LUN" which option should be used:
"Block-based"
"Thin Provisioning"
"File-based"
"Instant Allocation"