Oracle backup io down event

1. parameter explain BACKUP_TAPE_IO_SLAVES

If BACKUP_TAPE_IO_SLAVES=TRUE a single tape slave per channel is used.
This speeds up the backup if the bottleneck is in writing to tape;
it frees the channel process to continue processing rman input buffers
whilst the tape slave waits for IO completion.

2. run backup job when backup_tape_io_slaves set true

SQL> /

 INST   SID    SERIAL# USERNAME   PROGRAM                        MODULE                         MACHINE         CLIENT_INFO          SQL_ID           B_INST  B_SESS EVENT                                             S_WAIT SPID
----- ----- ---------- ---------- ------------------------------ ------------------------------ --------------- -------------------- --------------- ------- ------- --------------------------------------------- ---------- ------------------------
    1     8          5 SYS        sqlplus@orcldb (TNS V1-V3)     sqlplus@orcldb (TNS V1-V3)     orcldb                               6pduj1hhyxg0f                   SQL*Net message to client                              0 20258
    1    11          9 SYS                                                                                                                                           i/o slave wait                                         0 21267
    1    12          7 SYS                                                                                                                                           Backup: MML create a backup piece                     29 21281
    1    70         15 SYS        rman@orcldb (TNS V1-V3)        backup incr datafile           orcldb          rman channel=ch02                                    io done                                                0 21272
    1    72         23 SYS        rman@orcldb (TNS V1-V3)        backup incr datafile           orcldb          rman channel=ch00                                    imm op                                                 1 21258
    1   131         15 SYS                                                                                                                                           Backup: MML create a backup piece                      4 21260
    1   132         15 SYS                                                                                                                                           Backup: MML write backup piece                         0 21274
    1   199         25 SYS        rman@orcldb (TNS V1-V3)        backup incr datafile           orcldb          rman channel=ch03                                    imm op                                                 1 21279

8 rows selected.

SQL>

SQL> show parameter tape

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
backup_tape_io_slaves                boolean     TRUE
tape_asynch_io                       boolean     TRUE
SQL>

3. run backup job when backup_tape_io_slaves set true

SQL> /

 INST   SID    SERIAL# USERNAME   PROGRAM                        MODULE                         MACHINE         CLIENT_INFO          SQL_ID           B_INST  B_SESS EVENT                                             S_WAIT SPID
----- ----- ---------- ---------- ------------------------------ ------------------------------ --------------- -------------------- --------------- ------- ------- --------------------------------------------- ---------- ------------------------
    1   191          3 SYS        sqlplus@orcldb (TNS V1-V3)     sqlplus@orcldb (TNS V1-V3)     orcldb                               6pduj1hhyxg0f                   SQL*Net message to client                              0 22019
    1    10         53 SYS        rman@orcldb (TNS V1-V3)        backup incr datafile           orcldb          rman channel=ch02                                    Backup: MML create a backup piece                     16 22138
    1    71          9 SYS        rman@orcldb (TNS V1-V3)        backup incr datafile           orcldb          rman channel=ch03                                    Backup: MML create a backup piece                     15 22139
    1   131          5 SYS        rman@orcldb (TNS V1-V3)        backup incr datafile           orcldb          rman channel=ch00                                    Backup: MML write backup piece                         0 22136
    1   198          5 SYS        rman@orcldb (TNS V1-V3)        backup incr datafile           orcldb          rman channel=ch01                                    Backup: MML create a backup piece                     16 22137

SQL>

SQL> show parameter tape

NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
backup_tape_io_slaves                boolean     FALSE
tape_asynch_io                       boolean     TRUE
SQL>

4. conclusion.

The ‘io done’ wait event means that the database had to wait on I/O slaves to complete tape write.
Since you have the BACKUP_TAPE_IO_SLAVES parameter set to TRUE your backup is using I/O slaves.
Your backup process is waiting on those slaves to complete a request.
This should only impact your backup operation and not impact your end users, meaning unless you have a performance issue with your backup,
you can safely ignore this wait event.