PowerFlex: Volume I/O fails due to SDC connectivity issues

 SDC unable to communicate with SDSs.

Scenario

Networking issue impacts SDC connectivity to the SDSs.

Symptoms

This condition usually manifests as volume read/write failures:
 

2018-06-29T12:14:21.921Z cpu7:66759)ScsiDeviceIO: 2962: Cmd(0x439d96897a40) 0x28, CmdSN 0x85 from world 4873945 to dev "eui.4b20207776a7ba9773e9beb200000005" failed H:0x0 D:0x2 P:0x0 Valid sense data: 0x4 0x0 0x0.

2018-06-29T12:14:28.798Z cpu9:66759)ScsiDeviceIO: 2962: Cmd(0x439d9c113b00) 0x2a, CmdSN 0x800e003f from world 2218964 to dev "eui.4b20207776a7ba9773e9beb200000005" failed H:0x0 D:0x2 P:0x0 Valid sense data: 0x4 0x0 0x0.

2018-06-29T12:14:47.100Z cpu50:66759)ScsiDeviceIO: 2962: Cmd(0x439d8cd34880) 0x88, CmdSN 0xf1 from world 4873945 to dev "eui.4b20207776a7ba9773e9beb200000005" failed H:0x0 D:0x2 P:0x0 Valid sense data: 0x4 0x0 0x0.

2018-06-29T12:15:27.243Z cpu11:66759)ScsiDeviceIO: 2962: Cmd(0x439d9c0fc800) 0x8a, CmdSN 0x800e0070 from world 210279 to dev "eui.4b20207776a7ba9773e9beb200000005" failed H:0x0 D:0x2 P:0x0 Valid sense data: 0x4 0x0 0x0.

The preceding shows one of each SCSI opcode representing either read or write operations. 

Any of the above outputs may be in logs, not necessarily all. 

The scini module returns the same "020/400" SCSI sense information, which translates to "Hardware Error." 

Impact

Volume access is lost until connectivity is restored.

Generally, this is because of a loss of communication between the SDC and one or more SDS. 

It can also be caused by DU events, i.e. MDM_DATA_FAILED, or rejected/failed IOs due to errors on an SDS. 

SDC-SDS connectivity must be restored for volume I/O to succeed.

MDM_DATA_FAILED situations must be cleared.