tar failures will not always result in overall failure

If you use compress=gzip (or similar) and the tar portion of the backup fails, the overall run_command will return as successful, since the gzip portion succeeds (even if tar bails out)

For example (slightly scrubbed):

...
/bin/tar: server/data/example/table.ibd: File shrank by 28835840 bytes; padding with zeros
/bin/tar: server/data/example/table.ibd: File shrank by 7328165888 bytes; padding with zeros
/bin/tar: server/data/innodb1: File shrank by 4951052288 bytes; padding with zeros
/bin/tar: Error exit delayed from previous errors 13.1%
20091101 01:26:05 Info: DONE: create tar archive
20091101 01:26:05 Info: Cleaning up...
...

In this case, memory failure on the server ended up causing tar to completely bail out yet the overall process returned as successful.

We have switched to using compress="" and using tararg=cfz to eliminate the extra pipe.