NAME

       nbdkit-delay-filter - nbdkit delay filter

SYNOPSIS

        nbdkit --filter=delay plugin [plugin-args ...]
                 delay-read=DELAY
                 delay-write=DELAY
                 delay-zero=DELAY
                 delay-trim=DELAY
                 delay-extents=DELAY
                 delay-cache=DELAY
                 delay-open=DELAY
                 delay-close=DELAY
                 delay-fast-zero=BOOL

        nbdkit --filter=delay plugin rdelay=DELAY wdelay=DELAY [plugin-args...]

DESCRIPTION

       "nbdkit-delay-filter" is a filter for nbdkit(1) that delays read and write requests.  This is used to
       simulate a slow or remote server, or to test certain kinds of race conditions in Linux.  To limit server
       bandwidth use nbdkit-rate-filter(1) instead.  To simulate a spinning disk see nbdkit-spinning-filter(1).

EXAMPLES

       Delays reads and writes by 100ms:

        nbdkit --filter=delay file disk.img rdelay=100ms wdelay=100ms

       Delay only zero operations by 1 second, nothing else is affected:

        nbdkit --filter=delay file disk.img delay-zero=1

DELAY FORMAT

       In nbdkit ≥ 1.40, nbdkit_parse_delay(3) is used to parse the delay parameters, so a wide variety of
       formats are accepted, such as:

       delay-read=1.5
       delay-write=100ms
       delay-zero=1.2μs
       delay-trim=1000ns

       In nbdkit ≤ 1.38, only a whole number of seconds, or a whole number of milliseconds (if suffixed by "ms")
       were allowed.

PARAMETERS

       delay-cache=DELAY
           (nbdkit ≥ 1.14)

           Delay advisory cache operations by "DELAY".

       delay-close=DELAY
           (nbdkit ≥ 1.28)

           Delay  close (client disconnection) by "DELAY".  This can also cause server shutdown to be delayed if
           clients are connected at the time.  This only  affects  clients  that  gracefully  disconnect  (using
           "NBD_CMD_DISC"  / libnbd function nbd_shutdown(3)).  Clients that abruptly disconnect from the server
           cannot be delayed.

       delay-extents=DELAY
           (nbdkit ≥ 1.12)

           Delay block status (extents) operations by "DELAY".

       delay-fast-zero=BOOL
           (nbdkit ≥ 1.16)

           The NBD specification documents an extension called fast zero, in which the client may request that a
           server should reply with "ENOTSUP" as soon as possible if the zero operation offers no  real  speedup
           over  a corresponding write.  By default, this parameter is true, and fast zero requests are serviced
           by the plugin after the same delay as any other zero request; but setting  this  parameter  to  false
           instantly fails a fast zero response without waiting for or consulting the plugin.

       delay-open=DELAY
           (nbdkit ≥ 1.28)

           Delay open (client connection) by "DELAY".

       delay-read=DELAY
       rdelay=DELAY
           Delay read operations by "DELAY".

           The two forms "delay-read" and "rdelay" work identically.

       delay-trim=DELAY
           (nbdkit ≥ 1.10)

           Delay trim/discard operations by "DELAY".

       delay-write=DELAY
           Delay write operations by "DELAY".

       delay-zero=DELAY
           (nbdkit ≥ 1.10)

           Delay zero operations by "DELAY".  See also the "delay-fast-zero" option.

       wdelay=DELAY
           Delay  write,  zero  and  trim  operations  by  "DELAY".  (This is the same as setting "delay-write",
           "delay-zero" and "delay-trim" options together.)

FILES

       $filterdir/nbdkit-delay-filter.so
           The filter.

           Use "nbdkit --dump-config" to find the location of $filterdir.

VERSION

       "nbdkit-delay-filter" first appeared in nbdkit 1.2, based on earlier "rdelay"  and  "wdelay"  options  in
       nbdkit-file-plugin(1).

SEE ALSO

       nbdkit(1),  nbdkit-filter(3),  nbdkit-pause-filter(1),  nbdkit-rate-filter(1), nbdkit-spinning-filter(1),
       nbdkit_parse_delay(3).

AUTHORS

       Richard W.M. Jones

COPYRIGHT

       Copyright Red Hat

LICENSE

       Redistribution and use in source and binary forms, with or without modification, are  permitted  provided
       that the following conditions are met:

       •   Redistributions  of  source  code must retain the above copyright notice, this list of conditions and
           the following disclaimer.

       •   Redistributions in binary form must reproduce the above copyright notice, this list of conditions and
           the following disclaimer in the documentation and/or other materials provided with the distribution.

       •   Neither the name of Red Hat nor the names of its contributors may  be  used  to  endorse  or  promote
           products derived from this software without specific prior written permission.

       THIS  SOFTWARE  IS  PROVIDED BY RED HAT AND CONTRIBUTORS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
       INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND  FITNESS  FOR  A  PARTICULAR
       PURPOSE  ARE  DISCLAIMED.  IN  NO EVENT SHALL RED HAT OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
       INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,  PROCUREMENT  OF
       SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
       ON  ANY  THEORY  OF  LIABILITY,  WHETHER  IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
       OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
       DAMAGE.

nbdkit-1.42.9                                      2025-11-07                             nbdkit-delay-filter(1)