When the save starts, FDDRL stops all write I/Os for all disks of the pubset at the same time. The disks of the pubset are then as consistent with each other as mirror disks after splitting. As soon as a disk has been saved, FDDRL cancels the write lock for precisely this disk. Only when all disks have been saved does FDDRL cancel the write lock for the pubset.
During the write lock all the tasks in the system which execute write operations on the home pubset are placed in a wait state (VPASS) until the online save has been completed. Access to the PAGING file and MSCF access to the watchdog file are excluded from this.
FDDRL uses the F5 label from a storage area of the Allocator to save the disk, and consequently only the disk's allocated areas are saved.
FDDRL reduces the save scope by excluding disk areas with large files which are unimportant for the restoration (SYS.PAGING, SNAPFILE, SLEDFILE) from the save.
The time limit (TIME-LIMIT operand) determines the maximum time the write lock will apply for the home pubset. 1 to 120 minutes can be set; the default value is 5 minutes. If the time limit is reached before the end of the online save, FDDRL cancels the write lock for the home pubset, but continues the save. In this case the save will be inconsistent and unusable for restoration. However, the information about the time and space requirements of the save can be evaluated for subsequent saves.
Effects of the write lock
Tasks are also locked after a file has been read if the access date is updated in the file catalog (ACCESS-DATE) when the file is closed (e.g. when reading with /SHOW-FILE).
Indirect lock
Tasks can also be locked indirectly during the write lock because they request services from server tasks which are themselves locked. The indirectly locked tasks as a rule then wait in a communication bourse.
CONSLOG logging
Console messages are initially collected in an I/O buffer and then written to the CONSLOG file by the CLOG task block by block. As it is not possible to write the CONSLOG file during the online save, the CLOG task waits (with VPASS in PPAM). All messages for CONSLOG being buffered.
When more than 32 messages have been buffered per task, the message processing (TYPIO) also places the reporting task in a wait state (VPASS in the ECTYP module). Systems support should therefore as far as possible restrict the message output to console during an online save (e.g. switch off BCAM monitoring).