Merge branch master from git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

[sfrench/cifs-2.6.git] / Documentation / admin-guide / device-mapper / delay.rst

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+========
+dm-delay
+========
+
+Device-Mapper's "delay" target delays reads and/or writes
+and maps them to different devices.
+
+Parameters::
+
+    <device> <offset> <delay> [<write_device> <write_offset> <write_delay>
+                              [<flush_device> <flush_offset> <flush_delay>]]
+
+With separate write parameters, the first set is only used for reads.
+Offsets are specified in sectors.
+Delays are specified in milliseconds.
+
+Example scripts
+===============
+
+::
+
+       #!/bin/sh
+       # Create device delaying rw operation for 500ms
+       echo "0 `blockdev --getsz $1` delay $1 0 500" | dmsetup create delayed
+
+::
+
+       #!/bin/sh
+       # Create device delaying only write operation for 500ms and
+       # splitting reads and writes to different devices $1 $2
+       echo "0 `blockdev --getsz $1` delay $1 0 0 $2 0 500" | dmsetup create delayed