nbdkit-delay-filter - nbdkit delay filter
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...]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).
Delays reads and writes by 100ms:
nbdkit --filter=delay file disk.img rdelay=100ms wdelay=100msDelay only zero operations by 1 second, nothing else is affected:
nbdkit --filter=delay file disk.img delay-zero=1In nbdkit ≥ 1.40, nbdkit_parse_delay(3) is used to parse the delay parameters, so a wide variety of formats are accepted, such as:
In nbdkit ≤ 1.38, only a whole number of seconds, or a whole number of milliseconds (if suffixed by ms) were allowed.
Delay read operations by DELAY.
The two forms rdelay and delay-read work identically.
Delay write operations by DELAY.
(nbdkit ≥ 1.10)
Delay zero operations by DELAY. See also delay-fast-zero.
(nbdkit ≥ 1.10)
Delay trim/discard operations by DELAY.
(nbdkit ≥ 1.12)
Delay block status (extents) operations by DELAY.
(nbdkit ≥ 1.14)
Delay advisory cache operations by DELAY.
Delay write, zero and trim operations by DELAY.
(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.
(nbdkit ≥ 1.28)
Delay open (client connection) by 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.
The filter.
Use nbdkit --dump-config to find the location of $filterdir.
nbdkit-delay-filter first appeared in nbdkit 1.2, based on earlier rdelay and wdelay options in nbdkit-file-plugin(1).
nbdkit(1), nbdkit-filter(3), nbdkit-pause-filter(1), nbdkit-rate-filter(1), nbdkit-spinning-filter(1), nbdkit_parse_delay(3).
Richard W.M. Jones
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