Diferença entre amgtar e GNUTAR

Temos algumas centenas de sistemas fazendo backup em uma biblioteca de fitas usando AMANDA. Todos os dias recebemos um e-mail com uma longa lista de resultados de backup ESTRANHOS. Quase todos eles ocorrem porque um arquivo de log estava sendo gravado ou um cache baseado em arquivo estava sendo atualizado em um servidor web. Por exemplo (5 máquinas mostrando uma variedade de mensagens ESTRANHAS):

STRANGE DUMP DETAILS:
  /-- av1 / lev 2 STRANGE
  sendbackup: start [avion:/ level 2]
  sendbackup: info BACKUP=/bin/tar
  sendbackup: info RECOVER_CMD=/bin/tar -xpGf - ...
  sendbackup: info end
  ? /bin/tar: ./boot: directory is on a different filesystem; not dumped
  ? /bin/tar: ./dev: directory is on a different filesystem; not dumped
  ? /bin/tar: ./fs: directory is on a different filesystem; not dumped
  ? /bin/tar: ./proc: directory is on a different filesystem; not dumped
  ? /bin/tar: ./run: directory is on a different filesystem; not dumped
  ? /bin/tar: ./sys: directory is on a different filesystem; not dumped
  ? /bin/tar: ./wwwusers: directory is on a different filesystem; not dumped
  | /bin/tar: ./tmp/.X11-unix/X0: socket ignored
  | /bin/tar: ./tmp/gpg-v9zbWU/S.gpg-agent: socket ignored
  | Total bytes written: 795084800 (759MiB, 740KiB/s)
  sendbackup: size 776450
  sendbackup: end
  \--------
  /-- gitlab / lev 3 STRANGE
  sendbackup: start [gitlab:/ level 3]
  sendbackup: info BACKUP=/bin/tar
  sendbackup: info RECOVER_CMD=/bin/tar -xpGf - ...
  sendbackup: info end
  | /bin/tar: ./tmp/gitaly-ruby215330643/socket.0: socket ignored
  | /bin/tar: ./tmp/gitaly-ruby215330643/socket.1: socket ignored
  | /bin/tar: ./var/lib/gssproxy/default.sock: socket ignored
  ? /bin/tar: ./var/log/gitlab/gitlab-workhorse/current: file changed as we read it
  ? /bin/tar: ./var/log/gitlab/nginx/gitlab_access.log: file changed as we read it
  | /bin/tar: ./var/opt/gitlab/gitaly/gitaly.socket: socket ignored
  | /bin/tar: ./var/opt/gitlab/gitlab-rails/sockets/gitlab.socket: socket ignored
  | /bin/tar: ./var/opt/gitlab/gitlab-workhorse/socket: socket ignored
  | /bin/tar: ./var/opt/gitlab/postgresql/.s.PGSQL.5432: socket ignored
  | /bin/tar: ./var/opt/gitlab/redis/redis.socket: socket ignored
  | /bin/tar: ./var/spool/postfix/private/anvil: socket ignored
  | /bin/tar: ./var/spool/postfix/private/bounce: socket ignored
  | /bin/tar: ./var/spool/postfix/private/defer: socket ignored
  | /bin/tar: ./var/spool/postfix/private/discard: socket ignored
  | /bin/tar: ./var/spool/postfix/private/error: socket ignored
  | /bin/tar: ./var/spool/postfix/private/lmtp: socket ignored
  Look in the '/var/log/amanda/log.error/gitlab._.3.20180606231049.errout' file for full error messages
  \--------
  /-- haproxy00-127 / lev 3 STRANGE
  sendbackup: start [haproxy00-127:/ level 3]
  sendbackup: info BACKUP=/bin/tar
  sendbackup: info RECOVER_CMD=/bin/tar -xpGf - ...
  sendbackup: info end
  ? /bin/tar: ./var/log/messages: file changed as we read it
  Look in the '/var/log/amanda/log.error/haproxy00-127._.3.20180607003248.errout' file for full error messages
  \--------
  /-- imap00 /srv/dovecot lev 0 STRANGE
  sendbackup: start [imap00:/srv/dovecot level 0]
  sendbackup: info BACKUP=/bin/tar
  sendbackup: info RECOVER_CMD=/bin/tar -xpGf - ...
  sendbackup: info end
  ? /bin/tar: ./a1/Maildir/new/1528332018.M.imap00.example.com,S=6309,W=6430: File removed before we read it
  ? /bin/tar: ./a1/Maildir/new/1528335571.M.imap00.example.com,S=8299,W=8451: File removed before we read it
  ? /bin/tar: ./a2/Maildir/cur/1528306776.M.imap00.example.com,S=13517,W=13770\:2,Scd: File removed before we read it
  ? /bin/tar: ./a2/Maildir/cur/1528332257.M.imap00.example.com,S=22257,W=22562\:2,STcd: File removed before we read it
  ? /bin/tar: ./a3/Maildir/cur/1528287062.M.imap00.example.com,S=10343,W=10558\:2,: File removed before we read it
  ? /bin/tar: ./a3/Maildir/cur/1528297383.M.imap00.example.com,S=4179,W=4265\:2,: File removed before we read it
  ? /bin/tar: ./a3/Maildir/cur/1528312816.M.imap00.example.com,S=29364,W=29796\:2,: File removed before we read it
  ? /bin/tar: ./a3/Maildir/new/1528327304.M.imap00.example.com,S=52059,W=53029: File removed before we read it
  ? /bin/tar: ./a4/Maildir/.folder/dovecot.index.log.2: File removed before we read it
  ? /bin/tar: ./a4/Maildir/.Personal/dovecot.index.log.2: File removed before we read it
  ? /bin/tar: ./a4/Maildir/.Trash/cur/1527783480.M.imap00.example.com,S=31976,W=32433\:2,Sab: File removed before we read it
  ? /bin/tar: ./a4/Maildir/cur/1528336066.M.imap00.example.com,S=122100,W=124740\:2,ab: File removed before we read it
  ? /bin/tar: ./a4/Maildir/cur/1528337059.M.imap00.example.com,S=28553,W=28964\:2,ab: File removed before we read it
  Look in the '/var/log/amanda/log.error/imap00._srv_dovecot.0.20180606220538.errout' file for full error messages
  \--------
  /-- webserver1 / lev 2 STRANGE
  sendbackup: start [webserver1:/ level 2]
  sendbackup: info BACKUP=/bin/tar
  sendbackup: info RECOVER_CMD=/bin/tar -xpGf - ...
  sendbackup: info end
  ? /bin/tar: ./var/log/httpd/kemp_access_log: file changed as we read it
  ? /bin/tar: ./var/log/httpd/wiki.example.com_access_ssl.log: file changed as we read it
  ? /bin/tar: ./var/log/httpd/www.example.com_access.log: file changed as we read it
  ? /bin/tar: ./var/log/httpd/www.example.com_ssl_access_ssl.log: file changed as we read it
  Look in the '/var/log/amanda/log.error/webserver1._.2.20180607004437.errout' file for full error messages
  \--------

(brought to you by Amanda version 3.3.3)

Partes relevantes da nossa configuração atual:

define dumptype nocomp-root-tar {
    program "GNUTAR"
    comment "Root partitions with gtar"
    compress none
    estimate server
    priority low
    exclude list "/etc/amanda/amanda.exclude.list"
    auth "bsd"
}
define dumptype nocomp-user-tar {
    program "GNUTAR"
    comment "Non-root partitions with gtar"
    compress none
    estimate server
    priority medium
    exclude list "/etc/amanda/amanda.exclude.list"
    auth "bsd"
}

Não queremos excluir esses arquivos do backup apenas porque eles podem mudar ou desaparecer. Também não podemos desabilitar o servidor IMAP enquanto os backups estão em execução. Parece que posso alterar nossos sistemas para usar amgtarcomo método de backup, o que nos permitirá eliminar todas essas mensagens.

define application-tool app_amgtar {
    plugin "amgtar"

    property        "NORMAL" ": socket ignored$"
    property append "NORMAL" "file changed as we read it$"
    property append "NORMAL" ": directory is on a different filesystem; not dumped$"
    property append "NORMAL" ": File removed before we read it$"

}
define dumptype nocomp-root-amgtar {
    program "APPLICATION"
    application "app_amgtar"
    comment "Root partitions with amgtar"
    compress none
    estimate server
    priority low
    exclude list "/etc/amanda/amanda.exclude.list"
    auth "bsd"
}
...

Existem desvantagens para amgtar?

Será mais difícil recuperar backups mais antigos se fizermos essa alteração?

A documentação parece dizer que apenas GNUTARsuporta arquivos exclude list. Também suporta amgtar, pois usa GNUTARpor baixo?