windows_exporter/internal/collector/logical_disk/AGENTS.md

logical_disk collector

The collector reads the LogicalDisk PDH object with pdh.CounterTypeRaw. The object exists on every Windows host; no role is needed. It is multi-instance. These notes were recorded on a Windows Server 2025 (build 26100) Hyper-V guest.

• Instances are drive letters (C:), HarddiskVolumeN for volumes without a drive letter (here HarddiskVolume1 and HarddiskVolume4) and the aggregate _Total. internal/pdh drops _Total because the collector asks for pdh.InstancesAll. The other instances pass through the volume include and exclude regular expressions, and the instance name is the volume label.
• % Free Space is PERF_RAW_FRACTION. Its raw value equals Free Megabytes (49907) and its base is the volume size in megabytes (129254). The collector reads the base (,secondvalue) as the size in MB. Both values are in units of 1,048,576 bytes per the help text.
• The time counters share one raw value. % Disk Read Time, Avg. Disk Read Queue Length and the first value of Avg. Disk sec/Read were all 9858832; the write counters were all 11319205, and Avg. Disk sec/Transfer (21178037) is their sum. The raw value is the cumulative busy time in 100 ns ticks. internal/pdh converts the PERF_PRECISION_100NS_TIMER counters to seconds. The queue length and PERF_AVERAGE_TIMER values arrive in ticks and need the 1e-7 factor; the counter time base is 10 MHz here. The queue length counters duplicate the busy time, so the collector no longer reads them; the average queue length is rate(windows_logical_disk_{read,write}_seconds_total[5m]).
• Avg. Disk sec/Read, /Write and /Transfer are PERF_AVERAGE_TIMER. Their base is the operation count and equals Disk Reads/sec (3073), Disk Writes/sec (1698) and their sum (4771).
• % Idle Time is a cumulative 100 ns timer as well, not a percentage. On C: it was 115960642 ticks, about 11.6 seconds.
• Disk Read Bytes/sec and Disk Write Bytes/sec (PERF_COUNTER_BULK_COUNT) and the PERF_COUNTER_COUNTER rates are cumulative counts since boot.
• Current Disk Queue Length is an instantaneous snapshot (gauge) and was 0.
• Free Megabytes is a gauge. The collector code notes that Windows caches it; the volume is queried directly when possible.

Counter reference

Recorded on Windows Server 2025 (build 26100). Raw and Base are the first and second values that pdh.CounterTypeRaw returns for the sample instance.

LogicalDisk

Multi-instance. Instances: _Total, C:, HarddiskVolume1, HarddiskVolume4. Sample instance: C:.

Counters the collector reads:

Counter	Type	Raw	Base
% Disk Read Time	PERF_PRECISION_100NS_TIMER	9858832
% Disk Write Time	PERF_PRECISION_100NS_TIMER	11319205
% Free Space	PERF_RAW_FRACTION	49907	129254
% Idle Time	PERF_PRECISION_100NS_TIMER	115960642
Avg. Disk sec/Read	PERF_AVERAGE_TIMER	9858832	3073
Avg. Disk sec/Transfer	PERF_AVERAGE_TIMER	21178037	4771
Avg. Disk sec/Write	PERF_AVERAGE_TIMER	11319205	1698
Current Disk Queue Length	PERF_COUNTER_RAWCOUNT	0
Disk Read Bytes/sec	PERF_COUNTER_BULK_COUNT	131518976
Disk Reads/sec	PERF_COUNTER_COUNTER	3073
Disk Write Bytes/sec	PERF_COUNTER_BULK_COUNT	139952640
Disk Writes/sec	PERF_COUNTER_COUNTER	1698
Free Megabytes	PERF_COUNTER_RAWCOUNT	49907
Split IO/Sec	PERF_COUNTER_COUNTER	134

Not read by the collector:

• PERF_AVERAGE_BULK: Avg. Disk Bytes/Read, Avg. Disk Bytes/Transfer, Avg. Disk Bytes/Write
• PERF_COUNTER_100NS_QUEUELEN_TYPE: Avg. Disk Queue Length, Avg. Disk Read Queue Length (raw 9858832), Avg. Disk Write Queue Length (raw 11319205)
• PERF_COUNTER_BULK_COUNT: Disk Bytes/sec
• PERF_COUNTER_COUNTER: Disk Transfers/sec
• PERF_PRECISION_100NS_TIMER: % Disk Time