Miscellaneous limits

This topic provides values for other system limits, such as the number of basic disk pools, the size of a user space, and the size of a message queue.

Table 1. Miscellaneous limits
Miscellaneous limits	Value
Maximum system and I/O hardware configurations and capacities	See IBM i5 and iSeries™ Handbook.
Maximum number of DASD arms per partition	2047
Minimum number of DASD arms required for acceptable performance.	See Disk Arm Considerations in the Resource Library on the Performance Management web site.
Maximum number of connections to a disk unit in an Enterprise Storage Server^®	8
Maximum combined number of DASD arms and redundant connections to disk units¹	Approximately 2800
Maximum number of basic user ASPs	31
Maximum number of independent ASPs	223
Maximum number of logical partitions	See the Logical Partitions topic in the Information Center.
Maximum database size for Domino™	256 gigabytes
Maximum size of a user space²	16 773 120 bytes
Maximum size of a user index³	1 terabyte
Maximum size of a data queue or a user queue⁴	2 gigabytes
Maximum size of a message queue⁵	16 megabytes (approximately 75 000 messages)
Maximum number of new messages of any one message type on a message queue	Limited only by size of message queue
Maximum number of program messages that can be created in a job ⁶	4 294 967 293
Maximum number of records for each version of the history log	10 000 000
Maximum number of unique Volume IDs displayed/printed in Product Activity Log's Removable Media Lifetime Statistics for each Media Option	5000
Maximum number of input fields that can be specified for a display file	256
Maximum total size of concurrently used teraspace address ranges per job	Approximately 512 gigabytes
Range of user-defined double-byte characters that can be defined and maintained using the character generator utility (CGU) for Japanese	hexadecimal 6941 through 7FFE
Notes: The maximum number of DASD arms per partition is limited to 2047. Listed size is the maximum when the machine is allowed to choose the alignment. Absolute maximum size of a user space is 16 776 704 bytes. To create a 1 terabyte capable user index when using the QUSCRTUI API, specify a value of "1" for the Index Size Option. Otherwise, the size limit will be 4 gigabytes. The maximum size of a data queue that can be created through the data queue host server is 16 megabytes. Message queue QSYSOPR is shipped with a message queue full action of *WRAP. When the message queue is full, the oldest informational and answered messages are removed from the message queue to allow space for new messages to be added. If the removing of the informational and answered messages does not provide enough space, then unanswered inquiry messages are removed until there is space to add the new message. The default reply is sent before an unanswered inquiry message is removed. For more information, see the MSGQFULL parameter on the CHGMSGQ command. If the job has multiple threads, then the limit is the number of messages allowed in each thread.

Table 2. Interprocess Communication (IPC) limits
Interprocess Communication (IPC) limits	Value
Maximum number of Single UNIX^® Specification message queues on the system	2 147 483 46
Maximum size of a Single UNIX Specification message queue	16 773 120 bytes
Maximum size of a single message on a Single UNIX Specification message queue	65 535 bytes
Maximum number of semaphore sets on the system	2 147 483 646
Maximum number of semaphores per semaphore set	65 535
Maximum number of shared memory segments on the system	2 147 483 646
Maximum size of a teraspace shared memory segment	4 294 967 295 bytes
Maximum size of a resizeable teraspace shared memory segment	268 435 456 bytes
Maximum size of a nonteraspace shared memory segment	16 776 704 bytes
Maximum size of a resizeable nonteraspace shared memory segment	16 773 120 bytes