Comment 4 for bug 1403237

Another customer #49275 experienced backup failure after upgrade to 2.2.6/7.

The failure was during backup step, symptom was that log copying thread stuck at one sequence number and never move forward. Eventually, it reported error:

xtrabackup: error: log block numbers mismatch:
xtrabackup: error: expected log block no. 882663131, but got no. 891051735 from the log file.
xtrabackup: Error: xtrabackup_copy_logfile() failed.
innobackupex: got a fatal error with the following stacktrace: at /usr/bin/innobackupex line 2695
        main::wait_for_ibbackup_file_create('/tmp/xtrabackup_suspended_2') called at /usr/bin/innobackupex line 2715
        main::wait_for_ibbackup_suspend('/tmp/xtrabackup_suspended_2') called at /usr/bin/innobackupex line 1968
        main::backup() called at /usr/bin/innobackupex line 1592
innobackupex: Error: The xtrabackup child process has died at /usr/bin/innobackupex line 2695.

Innodb log file size is at 8G total, and server is PS 5.5.40. Test with Xtrabackup 2.1.9 always success, while with 2.2.7, half failure, half success. What Sergei explained above seems to apply to the case.