Add support for redirection replay of blktrace traces to another device

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 0ef7ca42120d175c3115207861f50b964a07958e..452e288b0279b76f7fd82997554973b58a3b5284 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -986,6 +986,30 @@ read_iolog=str     Open an iolog with the specified file name and replay the
                for how to capture such logging data. For blktrace replay,
                the file needs to be turned into a blkparse binary data
                file first (blkparse <device> -o /dev/null -d file_for_fio.bin).
+               
+replay_no_stall=int When replaying I/O with read_iolog the default behavior
+               is to attempt to respect the time stamps within the log and replay
+        them with the appropriate delay between IOPS.  By setting this variable
+        fio will not respect the timestamps and attempt to replay them as fast
+        as possible while still respecting ordering.  The result is the same
+        I/O pattern to a given device, but different timings.
+
+replay_redirect=str While replaying I/O patterns using read_iolog the
+               default behavior is to replay the IOPS onto the major/minor
+               device that each IOP was recorded from.  This is sometimes
+               undesireable because on a different machine those major/minor
+               numbers can map to a different device.  Changing hardware on
+               the same system can also result in a different major/minor
+               mapping.  Replay_redirect causes all IOPS to be replayed onto
+               the single specified device regardless of the device it was
+               recorded from. i.e. replay_redirect=/dev/sdc would cause all
+               IO in the blktrace to be replayed onto /dev/sdc.  This means
+               multiple devices will be replayed onto a single, if the trace
+               contains multiple devices.  If you want multiple devices to be
+               replayed concurrently to multiple redirected devices you must
+               blkparse your trace into separate traces and replay them with
+               independent fio invocations.  Unfortuantely this also breaks
+               the strict time ordering between multiple device accesses.
 
 write_bw_log=str If given, write a bandwidth log of the jobs in this job
                file. Can be used to store data of the bandwidth of the