ZARCSUMMARY(1)

NAME
zarcsummary - print ZFS ARC and subsystem statistics

SYNOPSIS
zarcsummary [-adghr] [-p page] [-s section]

DESCRIPTION
zarcsummary collects statistics from the running kernel and prints a human-readable report on the state of the ZFS Adaptive Replacement Cache (ARC) and several related subsystems. The output is a snapshot; for periodic sampling, use zarcstat(1) instead.

When invoked without arguments, zarcsummary prints all sections in sequence. A single section may be selected with the -s option.

The report is organized into the following sections:

arc Current and target ARC sizes, the split between the Most Recently Used (MRU) and Most Frequently Used (MFU) lists, overall hit and miss ratios, compression savings, and whether the ARC is experiencing memory pressure.

archits
    Breakdown of ARC hits and misses by demand reads versus prefetches and data versus metadata.

dmu Data Management Unit predictive prefetcher statistics, including stream hits, misses, and I/O issued ahead of and behind the current stream.

l2arc
    Level-2 ARC statistics for any cache devices attached to imported pools. This section only appears when an L2ARC device is present and covers bytes read and written, hit rates, and eviction activity.

spl Solaris Porting Layer memory allocator statistics. This section is only available on Linux.

tunables
    Current values of kernel tunables that govern ARC behavior, including zfs_arc_max and zfs_arc_min. Combining this section with -d adds a brief explanation of each tunable.

zil ZFS Intent Log statistics: committed transaction counts, flush requests to stable storage, and the byte-level split between normal vdevs and any separate log (SLOG) device.

OPTIONS

-a, --alternate
    Use an alternate layout for the tunables and SPL sections.

-d, --description
    Print a short description next to each tunable and SPL entry.

-h, --help
    Display a help message.

-g, --graph
    Print an ASCII graph of current ARC use and exit.

-p page, --page page
    Print a section by its legacy page number. Deprecated; use -s instead.

-r, --raw
    Dump all available data with minimal formatting.

-s section, --section section
    Print only the named section. See DESCRIPTION for the list of valid section names.

ENVIRONMENT

Linux
    Statistics are read from /proc/spl/kstat/zfs/.

FreeBSD
    Statistics are read via sysctl(3) from the vfs.zfs and kstat.zfs.misc trees. The py-sysctl package must be installed for zarcsummary to function.

EXIT STATUS

EXAMPLES
Print the full report:
    # zarcsummary

Display only ARC size and hit rate information:
    # zarcsummary -s arc

Show a visual overview of ARC health:
    # zarcsummary -g

Search for all statistics containing “hit”:
    # zarcsummary -r | grep hit

Review all tunables with their descriptions:
    # zarcsummary -d -s tunables

SEE ALSO
zarcstat(1), zpool-status(8)

HISTORY
zarcsummary originated as a Perl script called arc_summary, written by Ben Rockwood in 2008 for Solaris. Martin Matuska ported it to FreeBSD in 2010, and Jason J. Hellenthal took over maintenance. Scot W. Stevenson contributed a full rewrite in Python 3 in 2017, introducing the -g, -r, and -s options along with the section-based output layout. The tool was renamed from arc_summary to zarcsummary in 2025 to align with the OpenZFS command naming convention.

AUTHORS
This manual page was written by Christos Longros <chris.longros@gmail.com>.