1.\" SPDX-License-Identifier: CDDL-1.0 2.\" 3.\" This file and its contents are supplied under the terms of the 4.\" Common Development and Distribution License ("CDDL"), version 1.0. 5.\" You may only use this file in accordance with the terms of version 6.\" 1.0 of the CDDL. 7.\" 8.\" A full copy of the text of the CDDL should have accompanied this 9.\" source. A copy of the CDDL is also available via the Internet at 10.\" https://opensource.org/license/CDDL-1.0. 11.\" 12.\" Copyright (c) 2026 Christos Longros. All rights reserved. 13.\" 14.Dd March 14, 2026 15.Dt ZARCSUMMARY 1 16.Os 17. 18.Sh NAME 19.Nm zarcsummary 20.Nd print ZFS ARC and subsystem statistics 21.Sh SYNOPSIS 22.Nm 23.Op Fl adghr 24.Op Fl p Ar page 25.Op Fl s Ar section 26. 27.Sh DESCRIPTION 28.Nm 29collects statistics from the running kernel and prints a human-readable 30report on the state of the ZFS Adaptive Replacement Cache 31.Pq ARC 32and several related subsystems. 33The output is a snapshot; for periodic sampling, use 34.Xr zarcstat 1 35instead. 36.Pp 37When invoked without arguments, 38.Nm 39prints all sections in sequence. 40A single section may be selected with the 41.Fl s 42option. 43.Pp 44The report is organized into the following sections: 45.Bl -tag -offset Ds -width "tunables" 46.It Sy arc 47Current and target ARC sizes, the split between the Most Recently Used 48.Pq MRU 49and Most Frequently Used 50.Pq MFU 51lists, overall hit and miss ratios, compression savings, and whether the 52ARC is experiencing memory pressure. 53.It Sy archits 54Breakdown of ARC hits and misses by demand reads versus prefetches 55and data versus metadata. 56.It Sy dmu 57Data Management Unit predictive prefetcher statistics, including stream 58hits, misses, and I/O issued ahead of and behind the current stream. 59.It Sy l2arc 60Level-2 ARC statistics for any cache devices attached to imported pools. 61This section only appears when an L2ARC device is present and covers 62bytes read and written, hit rates, and eviction activity. 63.It Sy spl 64Solaris Porting Layer memory allocator statistics. 65This section is only available on Linux. 66.It Sy tunables 67Current values of kernel tunables that govern ARC behavior, including 68.Va zfs_arc_max 69and 70.Va zfs_arc_min . 71Combining this section with 72.Fl d 73adds a brief explanation of each tunable. 74.It Sy zil 75ZFS Intent Log statistics: committed transaction counts, flush requests 76to stable storage, and the byte-level split between normal vdevs and 77any separate log 78.Pq SLOG 79device. 80.El 81. 82.Sh OPTIONS 83.Bl -tag -width "-s" 84.It Fl a , -alternate 85Use an alternate layout for the tunables and SPL sections. 86.It Fl d , -description 87Print a short description next to each tunable and SPL entry. 88.It Fl h , -help 89Display a help message. 90.It Fl g , -graph 91Print an ASCII graph of current ARC use and exit. 92.It Fl p Ar page , Fl -page Ar page 93Print a section by its legacy page number. 94.Sy Deprecated ; 95use 96.Fl s 97instead. 98.It Fl r , -raw 99Dump all available data with minimal formatting. 100.It Fl s Ar section , Fl -section Ar section 101Print only the named section. 102See 103.Sx DESCRIPTION 104for the list of valid section names. 105.El 106. 107.Sh ENVIRONMENT 108.Bl -tag -width "FreeBSD" 109.It Sy Linux 110Statistics are read from 111.Pa /proc/spl/kstat/zfs/ . 112.It Fx 113Statistics are read via 114.Xr sysctl 3 115from the 116.Va vfs.zfs 117and 118.Va kstat.zfs.misc 119trees. 120The 121.Pa py-sysctl 122package must be installed for 123.Nm 124to function. 125.El 126. 127.Sh EXIT STATUS 128.Ex -std 129. 130.Sh EXAMPLES 131Print the full report: 132.Dl # zarcsummary 133.Pp 134Display only ARC size and hit rate information: 135.Dl # zarcsummary -s arc 136.Pp 137Show a visual overview of ARC health: 138.Dl # zarcsummary -g 139.Pp 140Search for all statistics containing 141.Dq hit : 142.Dl # zarcsummary -r | grep hit 143.Pp 144Review all tunables with their descriptions: 145.Dl # zarcsummary -d -s tunables 146. 147.Sh SEE ALSO 148.Xr zarcstat 1 , 149.Xr zpool-status 8 150. 151.Sh HISTORY 152.Nm 153originated as a Perl script called 154.Nm arc_summary , 155written by 156.An Ben Rockwood 157in 2008 for Solaris. 158.An Martin Matuska 159ported it to 160.Fx 161in 2010, and 162.An Jason J. Hellenthal 163took over maintenance. 164.An Scot W. Stevenson 165contributed a full rewrite in Python 3 in 2017, introducing the 166.Fl g , 167.Fl r , 168and 169.Fl s 170options along with the section-based output layout. 171The tool was renamed from 172.Nm arc_summary 173to 174.Nm zarcsummary 175in 2025 to align with the OpenZFS command naming convention. 176. 177.Sh AUTHORS 178This manual page was written by 179.An Christos Longros Aq Mt chris.longros@gmail.com . 180