Which TWO indicators should an administrator keep an eye on to determine if the storage...

The most direct evidence that storage capacity is approaching exhaustion is high filesystem utilization and explicit operating-system errors showing that no space remains. Sustained disk utilization above 90% is a practical warning threshold because the deployment has little headroom for database growth, index builds, temporary files, journal activity, or operational spikes. The errno:28 No space left on device message is even stronger evidence: the operating system rejected a write because the relevant filesystem could not allocate additional space. The other choices can correlate with workload growth but do not specifically prove a capacity problem. Query execution time can increase because of poor indexes, cache misses, lock or ticket contention, or CPU pressure. A rising document count says nothing about remaining free space without knowing document size, index size, and volume capacity. Low read/write ticket availability reflects storage-engine concurrency pressure rather than filesystem capacity. Administrators should therefore monitor disk-used and disk-free metrics, alert well before full utilization, and investigate any ENOSPC-style log events immediately. B and D are the two storage-capacity indicators.

Study Guide reference/topic:Performance Monitoring and Tuning - disk capacity, storage metrics, alerts, and diagnostic logs.

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