ioztat
ZFS dataset IO statistics
ioztat is to OpenZFS datasets what zpool-iostat(8) is to ZFS pools and vdevs.
Where zpool-iostat provides IO statistics for accesses to the lower level components
that make up a ZFS filesystem — the devices that underpin it and the mirrored, striped,
and parity-combined virtual devices these are part of — ioztat does so for the filesystems
and virtual block devices layered on top.
ioztat grew from a relatively modest Python script written by a few Reddit users,
with a few sorting options and not much else.
I added FreeBSD support to it, and then… well:
NAME
ioztat – display logical I/O statistics for ZFS datasets
SYNOPSIS
ioztat -V | --version
ioztat -h | --help
ioztat [-DeHINnoSxyz] [-c count] [-i interval] [-T u|d]
[-s name|operations|reads|writes|throughput|nread|nwritten]
[dataset ...] [interval [count]]
Yes, that is rather a lot of flags. Helpfully I also wrote a man page for it.
Here’s a quick demo, showing average per-second IO since bootup:
-% ioztat
operations throughput
dataset read write read write
------------------ ----- ----- ----- -----
zroot
ROOT
default 6 0 41.3K 13.4K
bastille 0 0 0 0
backups 0 0 0 0
cache 0 0 0 0
13.0-RELEASE 0 0 0 0
13.1-RELEASE 0 0 0 108
Sorted by operations:
-% ioztat -s operations
operations throughput
dataset read write read write
------------------------------------ ----- ----- ----- -----
zroot/ROOT/default 6 0 41.3K 13.4K
zroot/bastille/jails/freshbsd0/root 3 0 25.4K 2.89K
zroot/freshbsd/db/postgres 1 0 6.95K 833
zroot/freshbsd/db/elastic 0 0 567 698
zroot/var/log 0 0 506 132
Summing all child dataset statistics into their parents (-S), displaying
values per report interval rather than per-second (-I), suppressing display
of child datasets (-n), skipping the initial since-boot summary record (-y),
displaying extended, extended statistics, and setting the reporting interval
to ten seconds:
-% ioztat -SInyxx zroot 10
operations throughput opsize unlinks
dataset read write read write read write queue done
---------- ----- ----- ----- ----- ----- ----- ----- -----
zroot 35 19 50.0K 20.8K 1.43K 1.09K 2 2
---------- ----- ----- ----- ----- ----- ----- ----- -----
zroot 41 8 198K 17.3K 4.83K 2.16K 6 6
---------- ----- ----- ----- ----- ----- ----- ----- -----
zroot 1 4 330 352 330 88 1 1
---------- ----- ----- ----- ----- ----- ----- ----- -----
zroot 52 8 229K 34.4K 4.40K 4.30K 5 5
Other notable options include -o to overwrite earlier reports in the terminal so it
can be used as something of an iotop-alike tool, -z to omit inactive datasets,
and the -H and -e flags intended for use with scripting.
ioztat is available in the FreeBSD ports system under sysutils/py-ioztat.
Linux users are encouraged to do something with my ioztat-packages repository. I don’t use Linux, I’m not writing all this and making your packages for you.