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 operations: 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
       efficiency.

       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, including 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)