Catalyst 4500 Sup 7 DBL Drops

Question

Hallo Guy´s. 
I have a problem with a 4510 Switch with Sup 7 and VSS. sometimes i get from my management System a error message that i have drops. When i look at the Switch i see with a show interface the following output.
GigabitEthernet1/1/20 is up, line protocol is up (connected)
  Hardware is Gigabit Ethernet Port, address is fc5b.3981.00cb (bia fc5b.3981.00cb)
  Description: Uplink >> DEISSW28 > 0/49
  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 1000Mb/s, link type is auto, media type is 1000BaseSX
  input flow-control is off, output flow-control is off
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:03, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 33588
  Queueing strategy: Class-based queueing
  Output queue: 0/40 (size/max)
  5 minute input rate 3389000 bits/sec, 396 packets/sec
  5 minute output rate 1373000 bits/sec, 375 packets/sec
     259327531 packets input, 260486639929 bytes, 0 no buffer
     Received 2197702 broadcasts (1237454 multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 input packets with dribble condition detected
     687620273 packets output, 171964900087 bytes, 0 underruns
     0 output errors, 0 collisions, 6 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier
     0 output buffer failures, 0 output buffers swapped out
When i display the counters i see that i have DBL Drops:
Port InBytes InUcastPkts InMcastPkts InBcastPkts
Gi1/1/20 260445332225 257093813 1237385 960186
Port OutBytes OutUcastPkts OutMcastPkts OutBcastPkts
Gi1/1/20 171951485588 586491305 47531837 53564908
Port InPkts 64 OutPkts 64 InPkts 65-127 OutPkts 65-127
Gi1/1/20 169938 2535840 73860043 571805902
Port InPkts 128-255 OutPkts 128-255 InPkts 256-511 OutPkts 256-511
Gi1/1/20 15065293 22890554 3761375 4726098
Port InPkts 512-1023 OutPkts 512-1023
Gi1/1/20 2832564 3570926
Port InPkts 1024-1518 OutPkts 1024-1518 InPkts 1519-1548 OutPkts 1519-1548
Gi1/1/20 2133852 7956164 161468319 74102567
Port InPkts 1549-9216 OutPkts 1549-9216
Gi1/1/20 0 0
Port Tx-Bytes-Queue-1 Tx-Bytes-Queue-2 Tx-Bytes-Queue-3 Tx-Bytes-Queue-4
Gi1/1/20 3885776852 36149774 129367770 772345869
Port Tx-Bytes-Queue-5 Tx-Bytes-Queue-6 Tx-Bytes-Queue-7 Tx-Bytes-Queue-8
Gi1/1/20 430894369 32739589 141604609 166522564649
Port Tx-Drops-Queue-1 Tx-Drops-Queue-2 Tx-Drops-Queue-3 Tx-Drops-Queue-4
Gi1/1/20 0 0 1 0
Port Tx-Drops-Queue-5 Tx-Drops-Queue-6 Tx-Drops-Queue-7 Tx-Drops-Queue-8
Gi1/1/20 0 0 0 6
Port Dbl-Drops-Queue-1 Dbl-Drops-Queue-2 Dbl-Drops-Queue-3 Dbl-Drops-Queue-4
Gi1/1/20 0 0 0 0
Port Dbl-Drops-Queue-5 Dbl-Drops-Queue-6 Dbl-Drops-Queue-7 Dbl-Drops-Queue-8
Gi1/1/20 0 0 0 16787
Port Rx-No-Pkt-Buff RxPauseFrames TxPauseFrames PauseFramesDrop
Gi1/1/20 0 0 0 0
Port UnsupOpcodePause
Gi1/1/20 0
Port CrcAlign-Err Dropped-Bad-Pkts Collisions Symbol-Err
Gi1/1/20 0 0 0 0
Port Undersize Oversize Fragments Jabbers
Gi1/1/20 0 0 0 0
Port Single-Col Multi-Col Late-Col Excess-Col
Gi1/1/20 0 0 0 0
Port Deferred-Col False-Car Carri-Sen Sequence-Err
Gi1/1/20 0 0 0 0
Port RxIslTagFrames TxIslTagFrames RxDot1qTagFrames TxDot1qTagFrames
Gi1/1/20 0 0 257135468 683431783
On the Interface is auto qos configured. 
interface GigabitEthernet1/1/20
switchport trunk pruning vlan 2-1000
switchport mode trunk
auto qos trust
service-policy input AutoQos-4.0-Input-Policy
service-policy output AutoQos-4.0-Output-Policy
Comes this behavior from the qos? Where can i see wich traffic is assigned to queue 8?
Regards Stefan

Answer 1

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Yes, DBL is a (unique to) 4500 sup QoS feature.  Likely configured in your egress service-policy.
I don't recall the sup7 QoS architecture, but switches often provide fixed egress queues that you map traffic to via either CoS or ToS markings.  The QoS section of the User Guide, for your IOS version, should explain.