Fan reports a negative speed

SUMMARY

In general a negative fan speed indicates a faulty fan and it should be replaced, unless it is an absent fan, like FAN5 below.

ISSUE

Running the 'ipmiutil sensor -c' command for this issue most commonly shows symptoms like these below.   If a fan is present, and shows a sensor reading below the threshold (negative or otherwise), it indicates a problem with the fan itself, unless the fan was already absent. 

# ipmiutil sensor -c
ipmiutil ver 2.97
isensor: version 2.97
-- BMC version 3.26, IPMI version 2.0
ID | SDRType | Type |SNum| Name |Status| Reading
0004 | Full | Temperature | 11 | System Temp | OK | 24.00 C
0047 | Full | OEM(c0) | 12 | CPU Temp | 00 Low
008a | Full | Fan | 41 | FAN 1 | OK | 10390.00 RPM
00cd | Full | Fan | 42 | FAN 2 | BelowCrit | -2560.00 RPM
0110 | Full | Fan | 43 | FAN 3 | OK | 9835.00 RPM
0153 | Full | Fan | 44 | FAN 4 | OK | 9835.00 RPM
0196 | Full | Fan | 45 | FAN 5 | Absent | 0.00 na


If the fan was already absent (e.g. FAN 5), see the Notes below about updating firmware.
 

 

RESOLUTION

Note that if the fan previously reported a good reading and now reports a negative reading, the fan is faulty and replacing the fan will correct the problem.  

In most cases, the fan is the problem, not the firmware.  You can verify this by checking 'ipmiutil sel' and if there are fan events, then replace the fan.  Don't waste your time updating the firmware in these cases.  

If the negative fan speed is reported for a fan that is present (like Fan 2), then do these steps:

  1. Check the output of the 'ipmiutil sel -e' command for any Fan-related events:
    # ipmiutil sel -e
    ipmiutil ver 2.97
    isel: version 2.97
    -- BMC version 3.16, IPMI version 2.0
    SEL Ver 0 Support 03, Size = 512 records (Used=26, Free=486)
    RecId Date/Time_______ SEV Src_ Evt_Type___ Sens# Evt_detail - Trig [Evt_data]
    0001 01/08/15 14:33:48 MIN BMC Platform Security #51 Chassis Intru Chassis Intrusion 6f [f0 ff ff]
    0002 10/17/16 12:13:42 MIN BMC Fan #42 FAN 2 Lo Noncrit thresh actual=-2560.00 RPM, threshold=585.00 RPM
    0003 10/17/16 12:13:42 MAJ BMC Fan #42 FAN 2 Lo Crit thresh actual=-2560.00 RPM, threshold=400.00 RPM
    0004 10/17/16 12:13:42 CRT BMC Fan #42 FAN 2 Lo Unrec thresh actual=-2560.00 RPM, threshold=215.00 RPM
    0005 10/17/16 12:21:38 INF BMC Fan #42 FAN 2 LoU thresh OK now actual=1510.00 RPM, threshold=215.00 RPM
    0006 10/17/16 12:21:38 INF BMC Fan #42 FAN 2 LoC thresh OK now actual=1510.00 RPM, threshold=400.00 RPM
    0007 10/17/16 12:21:38 INF BMC Fan #42 FAN 2 LoN thresh OK now actual=1510.00 RPM, threshold=585.00 RPM
    0008 10/17/16 12:22:57 MIN BMC Fan #42 FAN 2 Lo Noncrit thresh actual=-2560.00 RPM, threshold=585.00 RPM
    0009 10/17/16 12:22:57 MAJ BMC Fan #42 FAN 2 Lo Crit thresh actual=-2560.00 RPM, threshold=400.00 RPM
    000a 10/17/16 12:22:57 CRT BMC Fan #42 FAN 2 Lo Unrec thresh actual=-2560.00 RPM, threshold=215.00 RPM
    000b 10/17/16 12:24:15 INF BMC Fan #42 FAN 2 LoU thresh OK now actual=1325.00 RPM, threshold=215.00 RPM
    000c 10/17/16 12:24:15 INF BMC Fan #42 FAN 2 LoC thresh OK now actual=1325.00 RPM, threshold=400.00 RPM
    000d 10/17/16 12:24:15 INF BMC Fan #42 FAN 2 LoN thresh OK now actual=1325.00 RPM, threshold=585.00 RPM
    000e 10/17/16 12:26:06 MIN BMC Fan #42 FAN 2 Lo Noncrit thresh actual=-2560.00 RPM, threshold=585.00 RPM
    000f 10/17/16 12:26:06 MAJ BMC Fan #42 FAN 2 Lo Crit thresh actual=-2560.00 RPM, threshold=400.00 RPM
    0010 10/17/16 12:26:06 CRT BMC Fan #42 FAN 2 Lo Unrec thresh actual=-2560.00 RPM, threshold=215.00 RPM
    
  2. If any FAN events are present as shown above, replace the indicated Fan (FAN 2 above). It is not recommended to upgrade the firmware in this case, as firmware will not fix a stopped fan.
  3. If you wish, you may also verify whether the fan is currently stopped by looking for '= 00' under the Hex column in the output for that fan by executing this command:
    ipmiutil sensor -g fan

NOTES

On some motherboards, an absent fan (e.g FAN 5 below) may report a negative speed.  The ipmiutil command may provide output such as the following:

# ipmiutil sensor -c
ID | SDRType | Type |SNum| Name |Status| Reading
0004 | Full | Temperature | 11 | System Temp | OK | 25.00 C
0047 | Full | OEM(c0) | 12 | CPU Temp | 00 Low
008a | Full | Fan | 41 | FAN 1 | OK | 6690.00 RPM
00cd | Full | Fan | 42 | FAN 2 | OK | 5765.00 RPM
0110 | Full | Fan | 43 | FAN 3 | OK | 6875.00 RPM
0153 | Full | Fan | 44 | FAN 4 | OK | 6875.00 RPM
0196 | Full | Fan | 45 | FAN 5 | BelowCrit | -2560.00 RPM
01d9 | Full | Voltage | 21 | CPU Vcore | OK | 1.06 V
021c | Full | Voltage | 23 | +3.3VCC | OK | 3.31 V
025f | Full | Voltage | 22 | +12 V | OK | 12.19 V
02a2 | Full | Voltage | 24 | CPU DIMM | OK | 1.53 V
02e5 | Full | Voltage | 25 | +5 V | OK | 5.12 v
0328 | Full | Voltage | 26 | -12 V | OK | -12.29 V
036b | Full | Voltage | 50 | VBAT | OK | 3.15 V
03ae | Full | Voltage | 4f | +3.3VSB | OK | 3.31 V
03f1 | Full | Voltage | 27 | AVCC | OK | 3.31 V
0434 | Full | Platform Securi | 51 | Chassis Intru | OK | 0.00 na
0477 | Full | Power Supply | 55 | PS Status | 01 Present
ipmiutil sensor, completed successfully

The negative fan speed reporting for fans which are absent (like Fan 5 above), can be mitigated by upgrading the SuperMicro IPMI firmware to the current version.  However, the absent fan is not causing a problem, so upgrading IPMI firmware on a customer system should not be attempted.

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