In order to operate, SHC-OSD needs a fixed batch task which is automatically started by SHC-OSD when the subsystem is started. It is started with the standard job class (for batch under TSOS) and without any time limit. The task has the job name SHCUSERT. SHC-OSD dynamically generates further tasks in order to execute commands.
To support SHC-OSD operation, at least 512 MB of additional capacity must be defined in the paging area. If a number of SHC-OSD commands are run in parallel, the memory requirements may be double this size.
The ADDRESS-SPACE-LIMIT must be at least 512 MB for the user IDs TSOS and SYSROOT.
The SHC-OSD commands are executed in fork tasks of the SHCUSERT batch task. Fork tasks do not inherit the CPU-LIMIT=*NO setting of the batch tasks they generate. The standard job class setting of the TSOS ID is valid for the fork tasks. (For information on fork tasks, refer to the “C Library Functions” manual [4].)
The POSIX file system must be configured for the use of SHC-OSD.
40-200 MB of free disk space for logging files in the /shcosd must be available in the /var file system. Disk space requirements are largely dependent
on the number and size of logging files stored. The system administrator should delete or archive logging files regularly.
The SHC-OSD parameter file contains a setting for the automatic deletion of the logging file of SHC-OSD (see "Configuration of SHC-OSD").
SHC-OSD uses POSIX semaphores (variables which control access to a shared resource). At least 20 free semaphore records should be available for operation (see "POSIX" manuals [2] and [3]).
SHC-OSD uses up to two POSIX shared memory segments.
You are recommended not to use the POSIX functionality "Journaling for File Systems" when all the following conditions are fulfilled for the pubset on which POSIX is installed:
The pubset consists of multiple volumes
The volumes are configured for DRV
The pubset is mirrored locally or remotely
The mirrors for the pubset are to be split consistently with SHC-OSD commands using
HOLD-IO=*UNTIL-...
When "Journaling for File Systems" is used in POSIX, this can result in competing I/O activities which impede consistent splitting of the mirrors.