Solaris 8 Software Developer Supplement

Periodic Health Checks

A latent fault is one that does not show itself until some other action occurs. For example, a hardware failure occurring in a device that is a cold stand-by could remain undetected until a fault occurs on the master device. At this point, it will be discovered that the system now contains two defective devices and might be unable to continue operation.

Generally, latent faults that are allowed to remain undetected will eventually cause system failure. Without latent fault checking, the overall availability of a redundant system is jeopardized. To avoid this, a device driver must detect latent faults and report them in the same way as other faults.

The driver should ensure that it has a mechanism for making periodic health checks on the device. In a fault-tolerant situation in which the device can be the secondary or failover device, early detection of a failed secondary device is essential to ensure that it can be repaired or replaced before any failure in the primary device occurs.

Periodic health checks can: