Quotes from Brendan Gregg

Beyond 60% utilization, the average response time doubles. By 80%, it has tripled. As disk I/O latency is often the bounding resource for an application, increasing the average latency by double or higher can have a significant negative effect on application performance. This is why disk utilization can become a problem well before it reaches 100%, as it is a queueing system where requests (typically) cannot be interrupted and must wait their turn.

2. Methodology

However, if application A is opaque and application B provides a rich set of observability tools, it's very likely that application B will be the better choice in the long run.

which is a unique numeric identifier. A process contains one or more threads, which operate in the process address space and share the same file descriptors (state describing open files).

It was later updated2 and