A bossock fiber is a SW thread that processes a request received by non-HW accelerated file serving traffic. Bossock fibers are pooled and shared within a node. The default pool size is 384.
Bossock Fibers utilization can be monitored in the SMU Web Manager Performance Charts. Consistently high bossock fiber utilization can signal there are bottlenecks in the system. The most common bottleneck is under configured disk storage. Contact support if you experience this.