ziostat -- Report ZFS read I/O activity


ziostat [-hIMrzZ] [interval [count]]


The ziostat utility reports a summary of ZFS read I/O operations. It
first prints all activity since boot, then reports activity over a
specified interval.

When run from a non-global zone (NGZ), only activity from that NGZ can be
observed. When run from a the global zone (GZ), activity from the GZ and
all other NGZs can be observed.

This tool is useful for determining if disk I/O is a source of
application latency. Combined with vfsstat(8), ziostat(8) shows the
relative contribution of disk I/O latency to overall I/O (and therefore
application) latency.


The ziostat utility reports the following information:

r/s reads per second

kr/s kilobytes read per second

actv average number of ZFS read I/O operations being
handled by the disk

wsvc_t average wait time per I/O, in milliseconds

asvc_t average disk service time per I/O, in milliseconds

%b percent of time there is an I/O operation pending


The following options are supported:

-h Show help message and exit

-I Print results per interval, rather than per second (where

-M Print results in MB/s instead of KB/s

-r Show results in a comma-separated format

-z Hide zones with no read I/O activity

-Z Print results for all zones, not just the current zone



Specifies the length in seconds to pause between each interval report.
If not specified, ziostat will print a summary since boot and exit.


Specifies the number of intervals to report. Defaults to unlimited if
not specified.


iostat(8), vfsstat(8), mpstat(8)


This utility does not show any ZFS write I/O activity. Most write
operations are asynchronous, so the latency of those operations
committing to disk is much less important that read latency.

The output format from ziostat may change over time; use the
comma-separated output for a stable output format.

March 2024 ZIOSTAT(8)