banshee/linux-collection/linux/ssh/diskio

Disk activity of a Linux, by SSH

Returns, for each disk, the reads and writes per second, the read and write throughput, the mean wait of a read and of a write, and the share of time the disk was busy.

Versions

Generic: /sys/block and /proc/diskstats are written by the kernel the same way on Alpine, Debian and Fedora; a sector in /proc/diskstats is always 512 bytes.

How it works

The collector runs ls /sys/block (the whole disks) and cat /proc/diskstats (the counters of each disk and partition since boot).

Only the disks of /sys/block are measured: it never lists partitions, whatever their name (sda1, nvme0n1p1, mmcblk0p1).
Every value comes from counters over the interval between two runs: the first run is skipped, and a disk whose counters went backwards is left out of that run.
The mean wait is the time spent on reads (writes) divided by their number; a disk without reads (writes) in the interval has no wait value.
Nothing is written on the target.

Prerequisites

an SSH account for monitoring, without write rights;
the fingerprint of the server's host key, set in protocol:ssh:fingerprint (not needed when the Security settings trust the first SSH fingerprint presented).

Outputs

Name	Label	Unit	Per instance
`read-iops`	Reads	op/s	yes, per disk
`write-iops`	Writes	op/s	yes, per disk
`read-rate`	Read throughput	MiB/s	yes, per disk
`write-rate`	Write throughput	MiB/s	yes, per disk
`read-wait`	Mean read wait	ms	yes, per disk
`write-wait`	Mean write wait	ms	yes, per disk
`busy`	Busy time	%	yes, per disk

The waits count the time in the queue; the busy time is the share of time with at least one operation in progress.

By default, loop*, ram*, zram*, sr*, fd* and nbd* are left out; the selection is changed on the probe.

Watches

Name	Title	Kind	Defaults	Checked by default
`read-latency`	Slow reads	above a threshold, on `read-wait`	warning above 50 ms, critical above 200 ms, for 5 min	yes
`write-latency`	Slow writes	above a threshold, on `write-wait`	warning above 50 ms, critical above 200 ms, for 5 min	yes
`busy`	Disk saturated	above a threshold, on `busy`	warning above 90 %, for 10 min; no critical	no

Limits

busy only means something for a disk that serves one operation at a time: an SSD or NVMe at 100 % may still serve many more. That is why it is not checked.
LVM and RAID volumes (dm-*, md*) are measured beside the disks under them: their activity is counted twice, once per layer.