Rescue a Time Machine backup from a failing readonly volume

rsync_tm.sh

#!/bin/bash

if [ -z "$1" ] || [ -z "$2" ]
then
   echo "ERROR: must supply CLI arguments for source and destination paths" >&2 &&
     exit 1
fi

export SRCVOL="$1"
export DSTVOL="$2"

[ -d "${SRCVOL}/Backups.backupdb" ] ||
echo -n "$(date) waiting for ${SRCVOL}/Backups.backupdb" && 
until [ -d "${SRCVOL}/Backups.backupdb" ];
do
  echo -n .
  sleep 5;
done &&
echo && echo "$(date) found ${SRCVOL}/Backups.backupdb" 

[ -z "${TMPDIR}" ] && export TMPDIR="${DSTVOL}/.root.rsync_tm.$RANDOM"
([ -d "${TMPDIR}" ] || mkdir -p "${TMPDIR}") && echo "Using temporary directory: ${TMPDIR}" >&2

DATERE='[[:digit:]]{4}-[[:digit:]]{2}-[[:digit:]]{2}-[[:digit:]]{6}'

time \
  /System/Library/Extensions/TMSafetyNet.kext/Contents/Helpers/bypass \
    ls -d "${SRCVOL}/Backups.backupdb/"* | xargs -n1 -IBKVOL \
    find "BKVOL" -maxdepth 1 -type d | egrep "${DATERE}" | sort -n |
  while read line; do echo "'$line'"; done |
  (
    A=""
    B=""
    C=""
    while read qDir
    do
      A="$B"
      B="$qDir"
      HASHEDKEY="$( echo \#$A\#$B\#$C|md5)"
      tgtdir="$( echo $A|sed 's:'"${SRCVOL}"'/:'"${DSTVOL}"'/:' )"
      C="$( dirname "${tgtdir}" )"
      ([ -z "$A" ]||[ -z "$B"  ]||[ -z "$C" ]||[ -f "$TMPDIR/$HASHEDKEY.done" ]) || (
        echo tmrsync -avvHE --progress --specials \
            --temp-dir="$TMPDIR" --partial-dir="$TMPDIR" \
            --rsync-path='/var/root/tmrsync' \
            "$A" \
            "$B" \
            "$C/'" 
      ) | 
        bash && echo "Success: $A + $B --> $C'" | tee $TMPDIR/$HASHEDKEY.done|| exit $?
    done
  )

[ "$?" -eq 0 ] && rm -rf "${TMPDIR}"
echo "$(date) done" 

tmrsync

#!/bin/bash
# must be found via PATH for use

exec /System/Library/Extensions/TMSafetyNet.kext/Contents/Helpers/bypass /opt/local/bin/rsync $@

Use macports rsync because Apple + brew is behind.