zfsdist(8) System Manager's Manual zfsdist(8)
NAME
zfsdist - Summarize ZFS operation latency. Uses Linux eBPF/bcc.
SYNOPSIS
zfsdist [-h] [-T] [-m] [-p PID] [interval] [count]
DESCRIPTION
This tool summarizes time (latency) spent in common ZFS file opera-
tions: reads, writes, opens, and syncs, and presents it as a power-of-2
histogram. It uses an in-kernel eBPF map to store the histogram for ef-
ficiency.
This uses kernel dynamic tracing of the ZPL interface (ZFS POSIX
Layer), and will need updates to match any changes to this interface.
This is intended to work with the ZFS on Linux project:
http://zfsonlinux.org
Since this uses BPF, only the root user can use this tool.
REQUIREMENTS
CONFIG_BPF and bcc.
OPTIONS
-h Print usage message.
-T Don't include timestamps on interval output.
-m Output in milliseconds.
-p PID Trace this PID only.
EXAMPLES
Trace ZFS operation time, and print a summary on Ctrl-C:
# zfsdist
Trace PID 181 only:
# zfsdist -p 181
Print 1 second summaries, 10 times:
# zfsdist 1 10
1 second summaries, printed in milliseconds
# zfsdist -m 1
FIELDS
msecs Range of milliseconds for this bucket.
usecs Range of microseconds for this bucket.
count Number of operations in this time range.
distribution
ASCII representation of the distribution (the count column).
OVERHEAD
This adds low-overhead instrumentation to these ZFS operations, includ-
ing reads and writes from the file system cache. Such reads and writes
can be very frequent (depending on the workload; eg, 1M/sec), at which
point the overhead of this tool may become noticeable. Measure and
quantify before use.
SOURCE
This is from bcc.
https://github.com/iovisor/bcc
Also look in the bcc distribution for a companion _examples.txt file
containing example usage, output, and commentary for this tool.
OS
Linux
STABILITY
Unstable - in development.
AUTHOR
Brendan Gregg
SEE ALSO
zfssnoop(8)
USER COMMANDS 2016-02-12 zfsdist(8)
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