We have 3 nodes in a cluster . We upgraded the mariadb version from 10.1.25-MariaDB to 10.3.14 . The mysql upgrade was successful in single node and mysql is also up. But while doing SST in node2 after clean up the mysql directory. The SST failed with the following errors everytime .
node1-innobackupex-backup: xb_stream_write_data() failed.
node1innobackupex-backup: #007-innobackupex: Error writing file 'UNKNOWN' (Errcode: 32 "Broken pipe")
node1-innobackupex-backup:  mariabackup: Error: xtrabackup_copy_datafile() failed.
The same issue was created in
MDEV-18482 and it is closed. Please let us know if this is a bug with version issue whereas in 10.1.25 version the SST is working fine till now.