Performance Impact due to FCP Queue Depth Threshold Reached

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Category:: fas-systems

Specialty:: san

Last Updated:

Applies to

Any version of ONTAP

Issue

A production outage can occur in a SAN environment that is connected with NetApp storage in the backend. Hosts may report high latency, or that they cannot connect to storage at all.

Adapter resets may be displayed for ports on the filer.
The repeated STIO TPD cmd alloc failed messages indicate a queue full condition in the filer.
The initiator(s) seem to be overloading this port. Eventually, the adapter is reset because a terminate CTIO is sent to the firmware (probably for an ABTS) and after not receiving a response to it for some time, it is flagged as a hungcommand.
Hitting the queue full condition means the filer resources have been exhausted.
The filer cannot process IO in a timely manner until it can free up resources in theSCSI queue

The following is reported in the EMS logs:

Thu Aug 04 02:40:16 EDT [Filer1: fct_tpd_thread_1: fcp.io.status:debug]: STIO Adapter:0g LUN:13DROPPED Cmd[2A] from SID:240942 VP:2 on OXID:000766 RxEx 0xffffffff (cmd allocation exceeded)at 59908347756

Fri Aug 31 22:56:12 EDT [Filer1: fct_tpd_thread_3: fcp.io.status:debug]: STIO TPD cmd alloc threshold reached handle:3 taskflags:0 Active commands:1945 threshold:1945

Host may report different messages depending on the OS.
For VMWare:

2016-08-04T07:54:36.573Z cpu30:32859)NMP: nmp_ThrottleLogForDevice:2349: Cmd 0x1a(0x413680446300, 0) to dev "mpx.vmhba32:C0:T0:L0" on path "vmhba32:C0:T0:L0" Failed: H:0x0D:0x28 P:0x0 Valid sense data: 0x0 0x0 0x0. Act:NONE
2016-08-04T07:58:21.779Z cpu9:33712)NMP: nmp_ThrottleLogForDevice:2349: Cmd 0x88(0x412e80451080, 36817) to dev "naa.600a09803830345a785d46414548504d" on path"vmhba1:C0:T1:L34" Failed: H:0x0 D:0x8 P:0x0 Possible sense data: 0x0 0x0 0x0. Act:EVAL

For Windows

8/31/2018,22:55:7,454,Warning,WindowsHost1,ontapdsm,61141,"IO error: SCSI Queue FULL reported on LUN 0 on Path Id 03000002. The IO will be retried."

For RHEL:

Aug 21 10:55:31 hostname kernel: qla2xxx [0000:0e:00.0]-3820:1: QUEUE FULL detected.