[MacPorts] #49657: Incorrect behaviour of --append-verify (and --partial) options

[MacPorts]

#49657: Incorrect behaviour of --append-verify (and --partial) options
--------------------------+--------------------------------
 Reporter:  swordangel@…  |      Owner:  macports-tickets@…
     Type:  defect        |     Status:  new
 Priority:  Normal        |  Milestone:
Component:  ports         |    Version:  2.3.4
 Keywords:                |       Port:  rsync
--------------------------+--------------------------------
 OS X 10.11.1 El Capitan

 rsync version: 3.1.1

 I seem to have discovered a nasty bug with the `--append-verify` (and
 `--partial`) options of rsync.

 As far as I can understand, the whole point of `--append-verify` is that
 in case of interruption, rsync will leave the destination file in its
 current state so that it can be resumed at a later point.

 Consider, for example:
 - source volume: "`/Volume/DyingHDD`"
 - destination volume: "`/Volume/NewHDD`"

 Suppose I have a 2 GB file "`/Volume/DyingHDD/00027.MTS`" and my DyingHDD
 is really dying: its read speed has degraded to around 5 MB/s and it's so
 unstable that it can't read 10 GB without suddenly going offline (OS X
 would think that it has not been ejected cleanly).

 So I try to salvage whatever is on DyingHDD by doing "`rsync -av --append-
 verify --timeout=60 /Volume/DyingHDD/ /Volume/NewHDD/`". Now, a few
 hundred MBs into  00027.MTS, DyingHDD suddenly disappears. I would expect
 rsync to leave "`/Volume/NewHDD/00027.MTS`" at the few hundred MB mark and
 quit.

 But that's not what happened. Instead, rsync proceeded to fill
 "`/Volume/NewHDD/00027.MTS`" '''all the way to 2 GB''' at the '''full
 speed''' of NewHDD (about 150 MB/s), and leave its timestamp at the
 current system time.

 Output of rsync:
 {{{
 00027.MTS
   2,125,627,392 100%   29.94MB/s    0:01:07 (xfr#11, ir-chk=1083/66263)
 }}}

 So the next time I call "`rsync -av --append-verify --timeout=60
 /Volume/DyingHDD/ /Volume/NewHDD/`", rsync just '''skips over'''
 00027.MTS.

 `--partial` has a similar behaviour

 I somewhat doubt it's a general bug in rsync exists in all platforms. All
 of the Linux people that I have spoken to say that `--append-verify` does
 leave the file in its partial state on Linux.

-- 
Ticket URL: <https://trac.macports.org/ticket/49657>
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