freebsd-dev/cmd/zpool_influxdb

Influxdb Metrics for ZFS Pools

The zpool_influxdb program produces influxdb line protocol compatible metrics from zpools. In the UNIX tradition, zpool_influxdb does one thing: read statistics from a pool and print them to stdout. In many ways, this is a metrics-friendly output of statistics normally observed via the zpool command.

Usage

When run without arguments, zpool_influxdb runs once, reading data from all imported pools, and prints to stdout.

zpool_influxdb [options] [poolname]

If no poolname is specified, then all pools are sampled.

option	short option	description
--execd	-e	For use with telegraf's execd plugin. When [enter] is pressed, the pools are sampled. To exit, use [ctrl+D]
--no-histogram	-n	Do not print histogram information
--signed-int	-i	Use signed integer data type (default=unsigned)
--sum-histogram-buckets	-s	Sum histogram bucket values
--tags key=value[,key=value...]	-t	Add tags to data points. No tag sanity checking is performed.
--help	-h	Print a short usage message

Histogram Bucket Values

The histogram data collected by ZFS is stored as independent bucket values. This works well out-of-the-box with an influxdb data source and grafana's heatmap visualization. The influxdb query for a grafana heatmap visualization looks like:

field(disk_read) last() non_negative_derivative(1s)

Another method for storing histogram data sums the values for lower-value buckets. For example, a latency bucket tagged "le=10" includes the values in the bucket "le=1". This method is often used for prometheus histograms. The zpool_influxdb --sum-histogram-buckets option presents the data from ZFS as summed values.

Measurements

The following measurements are collected:

measurement	description	zpool equivalent
zpool_stats	general size and data	zpool list
zpool_scan_stats	scrub, rebuild, and resilver statistics (omitted if no scan has been requested)	zpool status
zpool_vdev_stats	per-vdev statistics	zpool iostat -q
zpool_io_size	per-vdev I/O size histogram	zpool iostat -r
zpool_latency	per-vdev I/O latency histogram	zpool iostat -w
zpool_vdev_queue	per-vdev instantaneous queue depth	zpool iostat -q

zpool_stats Description

zpool_stats contains top-level summary statistics for the pool. Performance counters measure the I/Os to the pool's devices.

zpool_stats Tags

label	description
name	pool name
path	for leaf vdevs, the pathname
state	pool state, as shown by zpool status
vdev	vdev name (root = entire pool)

zpool_stats Fields

field	units	description
alloc	bytes	allocated space
free	bytes	unallocated space
size	bytes	total pool size
read_bytes	bytes	bytes read since pool import
read_errors	count	number of read errors
read_ops	count	number of read operations
write_bytes	bytes	bytes written since pool import
write_errors	count	number of write errors
write_ops	count	number of write operations

zpool_scan_stats Description

Once a pool has been scrubbed, resilvered, or rebuilt, the zpool_scan_stats contain information about the status and performance of the operation. Otherwise, the zpool_scan_stats do not exist in the kernel, and therefore cannot be reported by this collector.

zpool_scan_stats Tags

label	description
name	pool name
function	name of the scan function running or recently completed
state	scan state, as shown by zpool status

zpool_scan_stats Fields

field	units	description
errors	count	number of errors encountered by scan
examined	bytes	total data examined during scan
to_examine	bytes	prediction of total bytes to be scanned
pass_examined	bytes	data examined during current scan pass
issued	bytes	size of I/Os issued to disks
pass_issued	bytes	size of I/Os issued to disks for current pass
processed	bytes	data reconstructed during scan
to_process	bytes	total bytes to be repaired
rate	bytes/sec	examination rate
start_ts	epoch timestamp	start timestamp for scan
pause_ts	epoch timestamp	timestamp for a scan pause request
end_ts	epoch timestamp	completion timestamp for scan
paused_t	seconds	elapsed time while paused
remaining_t	seconds	estimate of time remaining for scan

zpool_vdev_stats Description

The ZFS I/O (ZIO) scheduler uses five queues to schedule I/Os to each vdev. These queues are further divided into active and pending states. An I/O is pending prior to being issued to the vdev. An active I/O has been issued to the vdev. The scheduler and its tunable parameters are described at the [ZFS documentation for ZIO Scheduler] (https://openzfs.github.io/openzfs-docs/Performance%20and%20Tuning/ZIO%20Scheduler.html) The ZIO scheduler reports the queue depths as gauges where the value represents an instantaneous snapshot of the queue depth at the sample time. Therefore, it is not unusual to see all zeroes for an idle pool.

zpool_vdev_stats Tags

label	description
name	pool name
vdev	vdev name (root = entire pool)

zpool_vdev_stats Fields

field	units	description
sync_r_active_queue	entries	synchronous read active queue depth
sync_w_active_queue	entries	synchronous write active queue depth
async_r_active_queue	entries	asynchronous read active queue depth
async_w_active_queue	entries	asynchronous write active queue depth
async_scrub_active_queue	entries	asynchronous scrub active queue depth
sync_r_pend_queue	entries	synchronous read pending queue depth
sync_w_pend_queue	entries	synchronous write pending queue depth
async_r_pend_queue	entries	asynchronous read pending queue depth
async_w_pend_queue	entries	asynchronous write pending queue depth
async_scrub_pend_queue	entries	asynchronous scrub pending queue depth

zpool_latency Histogram

ZFS tracks the latency of each I/O in the ZIO pipeline. This latency can be useful for observing latency-related issues that are not easily observed using the averaged latency statistics.

The histogram fields show cumulative values from lowest to highest. The largest bucket is tagged "le=+Inf", representing the total count of I/Os by type and vdev.

zpool_latency Histogram Tags

label	description
le	bucket for histogram, latency is less than or equal to bucket value in seconds
name	pool name
path	for leaf vdevs, the device path name, otherwise omitted
vdev	vdev name (root = entire pool)

zpool_latency Histogram Fields

field	units	description
total_read	operations	read operations of all types
total_write	operations	write operations of all types
disk_read	operations	disk read operations
disk_write	operations	disk write operations
sync_read	operations	ZIO sync reads
sync_write	operations	ZIO sync writes
async_read	operations	ZIO async reads
async_write	operations	ZIO async writes
scrub	operations	ZIO scrub/scan reads
trim	operations	ZIO trim (aka unmap) writes

zpool_io_size Histogram

ZFS tracks I/O throughout the ZIO pipeline. The size of each I/O is used to create a histogram of the size by I/O type and vdev. For example, a 4KiB write to mirrored pool will show a 4KiB write to the top-level vdev (root) and a 4KiB write to each of the mirror leaf vdevs.

The ZIO pipeline can aggregate I/O operations. For example, a contiguous series of writes can be aggregated into a single, larger I/O to the leaf vdev. The independent I/O operations reflect the logical operations and the aggregated I/O operations reflect the physical operations.

The histogram fields show cumulative values from lowest to highest. The largest bucket is tagged "le=+Inf", representing the total count of I/Os by type and vdev.

Note: trim I/Os can be larger than 16MiB, but the larger sizes are accounted in the 16MiB bucket.

zpool_io_size Histogram Tags

label	description
le	bucket for histogram, I/O size is less than or equal to bucket value in bytes
name	pool name
path	for leaf vdevs, the device path name, otherwise omitted
vdev	vdev name (root = entire pool)

zpool_io_size Histogram Fields

field	units	description
sync_read_ind	blocks	independent sync reads
sync_write_ind	blocks	independent sync writes
async_read_ind	blocks	independent async reads
async_write_ind	blocks	independent async writes
scrub_read_ind	blocks	independent scrub/scan reads
trim_write_ind	blocks	independent trim (aka unmap) writes
sync_read_agg	blocks	aggregated sync reads
sync_write_agg	blocks	aggregated sync writes
async_read_agg	blocks	aggregated async reads
async_write_agg	blocks	aggregated async writes
scrub_read_agg	blocks	aggregated scrub/scan reads
trim_write_agg	blocks	aggregated trim (aka unmap) writes

About unsigned integers

Telegraf v1.6.2 and later support unsigned 64-bit integers which more closely matches the uint64_t values used by ZFS. By default, zpool_influxdb uses ZFS' uint64_t values and influxdb line protocol unsigned integer type. If you are using old telegraf or influxdb where unsigned integers are not available, use the --signed-int option.

Using zpool_influxdb

The simplest method is to use the execd input agent in telegraf. For older versions of telegraf which lack execd, the exec input agent can be used. For convenience, one of the sample config files below can be placed in the telegraf config-directory (often /etc/telegraf/telegraf.d). Telegraf can be restarted to read the config-directory files.

Example telegraf execd configuration

# # Read metrics from zpool_influxdb
[[inputs.execd]]
#   ## default installation location for zpool_influxdb command
  command = ["/usr/libexec/zfs/zpool_influxdb", "--execd"]

    ## Define how the process is signaled on each collection interval.
    ## Valid values are:
    ##   "none"    : Do not signal anything. (Recommended for service inputs)
    ##               The process must output metrics by itself.
    ##   "STDIN"   : Send a newline on STDIN. (Recommended for gather inputs)
    ##   "SIGHUP"  : Send a HUP signal. Not available on Windows. (not recommended)
    ##   "SIGUSR1" : Send a USR1 signal. Not available on Windows.
    ##   "SIGUSR2" : Send a USR2 signal. Not available on Windows.
  signal = "STDIN"

  ## Delay before the process is restarted after an unexpected termination
  restart_delay = "10s"

    ## Data format to consume.
    ## Each data format has its own unique set of configuration options, read
    ## more about them here:
    ## https://github.com/influxdata/telegraf/blob/master/docs/DATA_FORMATS_INPUT.md
  data_format = "influx"

Example telegraf exec configuration

# # Read metrics from zpool_influxdb
[[inputs.exec]]
#   ## default installation location for zpool_influxdb command
  commands = ["/usr/libexec/zfs/zpool_influxdb"]
  data_format = "influx"

Caveat Emptor

• Like the zpool command, zpool_influxdb takes a reader lock on spa_config for each imported pool. If this lock blocks, then the command will also block indefinitely and might be unkillable. This is not a normal condition, but can occur if there are bugs in the kernel modules. For this reason, care should be taken:
  • avoid spawning many of these commands hoping that one might finish
  • avoid frequent updates or short sample time intervals, because the locks can interfere with the performance of other instances of zpool or zpool_influxdb

Other collectors

There are a few other collectors for zpool statistics roaming around the Internet. Many attempt to screen-scrape zpool output in various ways. The screen-scrape method works poorly for zpool output because of its human-friendly nature. Also, they suffer from the same caveats as this implementation. This implementation is optimized for directly collecting the metrics and is much more efficient than the screen-scrapers.

Feedback Encouraged

Pull requests and issues are greatly appreciated at https://github.com/openzfs/zfs