I found that split(1) command is much easier to use for making a multiple volume tar ball with fixed volume size 100MB.
BEFORE: $ tar cMf /Volumes/webdav/backup01.tar /some/important/files/ -L 102400
(please do remember to use ‘n /Volumes/webdav/backup02.tar’ command and two return keystrokes to proceed to the next “volume”.)
AFTER: $ tar cf - /some/important/files/ | split -b 100m - /Volumes/webdav/backup01.tar.
(the final dot is important because it’s the prefix of multiple filenames we are trying to store at the remote server.)