1*27ae70b8SShawn McCarney# Multiple Chassis 2*27ae70b8SShawn McCarney 3*27ae70b8SShawn McCarney## Overview 4*27ae70b8SShawn McCarney 5*27ae70b8SShawn McCarneyA BMC-based system can contain one or more chassis. A chassis is typically a 6*27ae70b8SShawn McCarneyphysical enclosure that contains system components such as CPUs, fans, power 7*27ae70b8SShawn McCarneysupplies, and PCIe cards. 8*27ae70b8SShawn McCarney 9*27ae70b8SShawn McCarneyA chassis can be stand-alone, such as a tower or desktop. A chassis can also be 10*27ae70b8SShawn McCarneydesigned to be mounted in an equipment rack. 11*27ae70b8SShawn McCarney 12*27ae70b8SShawn McCarneyFor the `phosphor-power-sequencer` application, the term "single chassis system" 13*27ae70b8SShawn McCarneymeans the system type has a maximum configuration of one chassis. If the system 14*27ae70b8SShawn McCarneytype has a maximum configuration of multiple chassis, then it is considered a 15*27ae70b8SShawn McCarney"multiple chassis system" even if the current system only contains one chassis. 16*27ae70b8SShawn McCarney 17*27ae70b8SShawn McCarney## Differences between single and multiple chassis systems 18*27ae70b8SShawn McCarney 19*27ae70b8SShawn McCarney### System and chassis power state 20*27ae70b8SShawn McCarney 21*27ae70b8SShawn McCarneyIn a single chassis system, the system and chassis power state are identical. 22*27ae70b8SShawn McCarneyBoth are either on or off. 23*27ae70b8SShawn McCarney 24*27ae70b8SShawn McCarneyIn a multiple chassis system, each chassis has its own power state. Even if the 25*27ae70b8SShawn McCarneysystem is on, an individual chassis may be off. This can occur if that chassis 26*27ae70b8SShawn McCarneydoes not have input power or has a critical hardware problem. 27*27ae70b8SShawn McCarney 28*27ae70b8SShawn McCarneySee [Chassis Status](chassis_status.md) for more information. 29*27ae70b8SShawn McCarney 30*27ae70b8SShawn McCarney### Chassis power good faults 31*27ae70b8SShawn McCarney 32*27ae70b8SShawn McCarneyIf a single chassis system experiences a power good (pgood) fault, the system is 33*27ae70b8SShawn McCarneypowered off. 34*27ae70b8SShawn McCarney 35*27ae70b8SShawn McCarneyIf a multiple chassis system experiences a power good (pgood) fault in one 36*27ae70b8SShawn McCarneychassis, the system will be powered off and then powered on again without that 37*27ae70b8SShawn McCarneychassis. 38*27ae70b8SShawn McCarney 39*27ae70b8SShawn McCarneySee [Power Good Faults](pgood_faults.md) for more information. 40*27ae70b8SShawn McCarney 41*27ae70b8SShawn McCarney### Brownouts 42*27ae70b8SShawn McCarney 43*27ae70b8SShawn McCarneyIf a single chassis system that was powered on experiences a brownout, the 44*27ae70b8SShawn McCarneysystem will be powered off. 45*27ae70b8SShawn McCarney 46*27ae70b8SShawn McCarneyIf a multiple chassis system that was powered on experiences a brownout in one 47*27ae70b8SShawn McCarneychassis, the system will be powered off and then powered on again without that 48*27ae70b8SShawn McCarneychassis. 49*27ae70b8SShawn McCarney 50*27ae70b8SShawn McCarneySee [Power Loss](power_loss.md) for more information. 51*27ae70b8SShawn McCarney 52*27ae70b8SShawn McCarney### Blackouts 53*27ae70b8SShawn McCarney 54*27ae70b8SShawn McCarneyIf a single chassis system that was powered on experiences a blackout, the 55*27ae70b8SShawn McCarneysystem loses all power. It will be completely off until utility power is 56*27ae70b8SShawn McCarneyrestored. It may then automatically power on again depending on the Auto Power 57*27ae70b8SShawn McCarneyRestart settings. 58*27ae70b8SShawn McCarney 59*27ae70b8SShawn McCarneyIf a multiple chassis system that was powered on experiences a blackout in one 60*27ae70b8SShawn McCarneychassis, that chassis loses all power. The system will be powered off and then 61*27ae70b8SShawn McCarneypowered on again without that chassis. 62*27ae70b8SShawn McCarney 63*27ae70b8SShawn McCarneySee [Power Loss](power_loss.md) for more information. 64