Bandwidth I/O graph and packet capture mode

Is it possible to get an accurate and correct Bandwidth I/O graph without capturing full packet?

yes, as Wireshark uses the information about the frame length, stored in the pcap file for each frame.

In addition, if there is need for long capture time required, do you have recommendation or precaution?

Yes.

• reduce the amount of captured data by using 'strict' capture filters
• capture with dumpcap instead of Wireshark. Don't use tshark either. Both are rather analyzing tools than capture tools.
• If you want to capture with Wireshark (not recommended for a long period of time)
• add enough RAM to your capturing machine (2 Gig is 'nothing' nowadays ;-))
• use a 64 Bit OS, to be able to use that RAM
• reduce the captured frame size (option -s for tcpdump and/or dumpcap)

Regards
Kurt