You need to implement QoS on a Cisco MDS 9000 Series Switch Which type of traffic must you classify so that no frames are dropped?

iSCSI runs over TCP/IP, which includes built-in congestion control and retransmission, so occasional packet drops are recoverable and iSCSI is not the primary lossless classification concern.

Fibre Channel relies on a lossless transport model where buffer-to-buffer credits manage flow control and no frames are permitted to be dropped. On an MDS 9000, QoS must classify Fibre Channel traffic at the highest priority class to guarantee zero frame loss, since FC has no native retransmission mechanism for dropped frames.

CIFS is a file-level protocol transported over TCP/IP, which handles retransmission natively, making dropped packets non-fatal to the session.

NFS is a file-level protocol over TCP/IP with its own retransmission handling, so dropped packets do not result in unrecoverable data loss.