CompTIA Linux+ (XK0-006)TroubleshootingMedium
A system administrator is troubleshooting a server experiencing slow disk I/O. They run `iostat -x 2` and observe the following output for `/dev/sdb`:
- AThe disk has a high number of read operations per second but low write operations.
- BThe disk is heavily utilized and likely a bottleneck.
- CThe disk is idle, indicating the bottleneck is elsewhere.
- DThe disk has a high number of write operations per second but low read operations.
Show answer & explanationAnswer & explanation
Correct answer: B. The disk is heavily utilized and likely a bottleneck.
A `%util` value consistently close to 100% indicates that the disk is busy almost all the time handling I/O requests. This suggests the disk is saturated and is a significant bottleneck for system performance.
Why the other options are wrong
- A. While r/s and w/s are present, %util is the primary indicator of overall disk saturation, not the ratio of reads to writes.
- C. A %util of 98.50 is very high, indicating heavy activity, not idle.
- D. Similar to C, %util indicates overall busyness, regardless of the read/write mix.
iostat %util
The `%util` (or `% Utilization`) column in `iostat` output indicates the percentage of time the device was busy servicing I/O requests. A value near 100% suggests the disk is a bottleneck.
- Measures disk busyness, not throughput or IOPS directly.
- High `%util` (e.g., >80-90%) often implies disk saturation.
- Useful for identifying I/O bottlenecks in storage systems.
Memory trick: Utility percentage shows how busy the disk is.