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Fibre Channel (SAN)

Posts: 0

Slow drain device across IFLs

Hello Experts, Please find the attached SAN design, I have a typical latency because of slow drain in the ports I circled in red.

Affected ports are IFL ports connecting to backbone fabric from Edge fabric target.

I understand Latency bottleneck always gets detected only on the egress side of the port, means here the issue is now with some device misbehaving in "Edge fabric Target" . However, when i noticed "porterrshow" in target edge fabric, I dont see any of the ports having C3 discards due to timeout. Also, I do notice VC Link Init is OFF in Ex-ports in both Backbone Fabric , but I do see lot of Buffer credit zero errors in individual data virtual channels in the ports affecting with slow drain. VC 5 is having high credit zero errors.

Area Number:          1
Speed Level:          AUTO(HW)
Fill Word:            3(A-A then SW I-A)
AL_PA Offset 13:      OFF
Trunk Port            OFF
Long Distance         OFF
VC Link Init          OFF
Locked L_Port         OFF
Locked G_Port         OFF
Disabled E_Port       OFF
Locked E_Port         OFF
ISL R_RDY Mode        OFF
RSCN Suppressed       OFF


tim_rdy_pri         9324    Time R_RDY high priority
tim_txcrd_z         2483102019  Time TX Credit Zero (2.5Us ticks)
tim_txcrd_z_vc  0- 3:  120653  0       158792446  1040787423
tim_txcrd_z_vc  4- 7:  207597198  1075804299 0       0
tim_txcrd_z_vc  8-11:  0       0       0       0
tim_txcrd_z_vc 12-15:  0       0       0       0


1) May I know when VC Link Init is OFF, why there are BB credit zero errors in IFL ports and in individual VCs. Is that because VC Link Init enabled on ISL links???

2) I dont see any C3 Discards in any of the ports in Edge fabric target and all the ports are having credit recovery enabled. Could you please help me with further steps to troubleshoot this slow drain device issue??

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