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)