NAME

       nbdkit-delay-filter - nbdkit delay filter

SYNOPSIS

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

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

        nbdkit --filter=delay plugin [plugin-args ...]
                 delay-read=(SECS|NNms) delay-write=(SECS|NNms)
                 delay-zero=(SECS|NNms) delay-trim=(SECS|NNms)
                 delay-extents=(SECS|NNms) delay-cache=(SECS|NNms)
                 delay-fast-zero=BOOL

DESCRIPTION

       "nbdkit-delay-filter" is a filter that delays read and write requests by some seconds or
       milliseconds.  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.

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

PARAMETERS

       rdelay=SECS
       rdelay=NNms
       delay-read=SECS
       delay-read=NNms
           Delay read operations by "SECS" seconds or "NN" milliseconds.

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

       delay-write=SECS
       delay-write=NNms
           Delay write operations by "SECS" seconds or "NN" milliseconds.

       delay-zero=SECS
       delay-zero=NNms
           (nbdkit ≥ 1.10)

           Delay zero operations by "SECS" seconds or "NN" milliseconds.  See also delay-fast-
           zero.

       delay-trim=SECS
       delay-trim=NNms
           (nbdkit ≥ 1.10)

           Delay trim/discard operations by "SECS" seconds or "NN" milliseconds.

       delay-extents=SECS
       delay-extents=NNms
           (nbdkit ≥ 1.12)

           Delay block status (extents) operations by "SECS" seconds or "NN" milliseconds.

       delay-cache=SECS
       delay-cache=NNms
           (nbdkit ≥ 1.14)

           Delay advisory cache operations by "SECS" seconds or "NN" milliseconds.

       wdelay=SECS
       wdelay=NNms
           Delay write, zero and trim operations by "SECS" seconds or "NN" milliseconds.

       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.

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).

AUTHORS

       Richard W.M. Jones

COPYRIGHT

       Copyright (C) 2018 Red Hat Inc.

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.

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