Comment 3 for bug 1403237

The issue is following

Server is Percona Server 5.5 with log_file_size = 6G. There is no support for log files larger than 4G in total in MySQL 5.5.

Percona Server 5.5 does support log files larger than >4G. XtraBackup 2.1 based on PS 5.5 can handle such files.

MySQL 5.6 introduced support for large log files, but these files are not compatible with PS 5.5 log files. For example LOG_CHECKPOINT_OFFSET is stored at different offset.

This makes value of group->lsn_offset invalid in xtrabackup 2.2. Which then used in log_group_calc_lsn_offset to find an offset in log file to read from. So, xtrabackup log copying thread simply cannot position itself correctly in server log files.